1 . Some of the oldest living things on our remarkable planet are trees. The record holders are bristlecone pines (狐尾松) of the western United States, quite a few of which are known to be more than 3,000 years old. One individual, discovered in 2012, is estimated to be more than 5,060 years old, making it the oldest known non-clonal tree in the world!     1    : individuals across a number of other tree species have also been around for thousands of years.

So, how do trees survive for thousands of years?     2    . Undoubtedly, part of the answer lies in luck. Ancient trees have obviously not submitted to deadly diseases, pests, fires, droughts, windstorms, landslides, or the human axe in the centuries and centuries that they have quietly endured.

The other part of the answer has to do with how trees age. In fact, there is quite a debate about whether ancient trees can be considered “immortal (永生的)”. That is, will such trees ever die if they are not killed by an outside force? We may never know the answer to that, but, at the very least,     3    . While cell death is an important factor in the aging of humans and other animals, one study found little evidence of cell death in the ginkgo tree vascular cambium (银杏树维管形成层). In addition, a study of bristlecone pine pollen (花粉) found no significant increase in mutation (变异) rates with age, which is another factor associated with animal aging.     4    .

Older trees benefit greatly from having bodies made mostly of dead woody tissue. In fact, an old tree might be as much as 95 percent dead tissue! Given that it isn’t alive, wood does not require metabolic (新陈代谢的) activity to maintain it,     5    .

A．so an old tree doesn’t really need to do much to keep living

B．This is a question that has something to do with the good luck of trees

C．However, bristlecones are certainly not alone in terms of the oldest creatures

D．This is a fascinating question for biologists that does not yet have a settled answer

E．What’s more, some ancient trees have superior chemical defenses against pests and diseases

F．which means that trees can survive everywhere without being limited by external and internal conditions

G．we know that ancient trees age in ways that are dramatically different from the ways that most animals and even other plants age

2 . Under a midday summer sun in California’s Sacramento Valley, rice farmer Peter Rystrom walks across a dusty and bare plot of land, dry soil crunching (碎裂) beneath each step. In a typical year, he’d be walking across green rice fields in inches of water. But today the soil is dry and baking in the 35℃ heat. It hasn’t rained for 4 weeks in a row.

“Climate change is expected to worsen the state’s extreme swings in rainfall,” researchers reported in Nature Climate Change in 2018. Low water levels in rivers have forced farmers like Rystrom, whose family has been growing rice on this land for four generations, to reduce their water use.

“If we lose our rice crops, we have to deal with severe food crisis. Climate change is already threatening rice-growing regions around the world. This is not a future problem. This is happening now,” says plant geneticist Pamela Ronald of the University of California, Davis, who identifies genes in rice that help the plant stand up to dryness, disease, flood, etc.

To save and even boost production, rice growers, engineers and researchers have turned to water-saving irrigation (灌溉) routines. Building canal systems and reservoirs (水库) can help farmers dampen their fields. But for some, the solution to rice’s climate-related problems lies in enhancing the plant itself. They hold that establishing rice gene banks that store hundreds of thousands of rice varieties ready to be bred into new, dryness-tolerant varieties is more practical and effective. Solutions may be hidden in the DNA of those older breeds.

Three decades have passed since its initial development, and some researchers are looking beyond the genetic variability preserved in rice gene banks, searching instead for useful genes from other species, including plants and bacteria. But picking genes from one species and putting them into another, or genetic recombination, remains debatable. The most famous example of genetically changed rice is Golden Rice (GR). “Looking ahead, it will be crucial for countries to embrace GR rice. But it will take time,” says Ismail, principal scientist at IRRI,

1. What problem does Rystrom have to deal with?

A．Thirst.

B．Drought.

C．Hot sun.

D．Dusty weather.

2. What can be inferred from Para. 3?

A．Downtrend of rice-growing areas is severe now.

B．Climate change is a threatening factor in the future.

C．Humans will face starvation if crop failure happens.

D．Food crisis is a common occurrence around the world.

3. What’s the purpose of setting up gene banks?

A．To store as many seeds as possible.	B．To cultivate climate-adapted varieties.
C．To improve the efficiency of breeding.	D．To show the technology of gene mapping.

4. What’s Ismail’s opinion about GR?

A．Favourable.

B．Impractical.

C．Disapproving.

D．Insecure.