1 . Most animals living in crowded conditions have particularly strong immune systems, so it long puzzled researchers that honeybees do not.

Part of the answer, discovered in 2015, is that queen bees vaccinate their eggs by moving parts of proteins from disease-causing pathogens to them before they are laid. These act as antigens to trigger the development of a protective immune response in the developing young. But that observation raises the question of how the queen receives her antigen supply in the first place? Dr. Harwood wondered if the nurse bees were taking in parts of pathogens and passing them to royal jelly they were producing while eating the food brought to the hive.

To test this idea, he teamed up with a group at the University of Helsinki, in Finland, led by Dr Heli Salmela. Together, they collected about 150 nurse bees and divided them among six queenless mini hives equipped with baby bees to look after. Instead of honey, they fed the nurses on sugar water, and for three of the hives they added P. larvae, a bacterium causing a hive-killing disease, to the sugar water.

In this case, to stop such an infection happening, Dr Harwood and Dr Salmela heat-treated the pathogens and so killed them in advance. They also labelled the dead bacteria with a fluorescent dye, to track them easily. And, sure enough, it was confirmed that parts of P. larvae were getting into royal jelly released by those bees which had been fed with the sugar water containing that.

All told, these findings suggest that nurse bees are indeed, through their royal jelly, passing antigens onto the queen for vaccinating her eggs. They also mean the nurses are vaccinating baby bees as well, because baby bees, too, receive royal jelly for the first few days after they come out.

1. What does the underlined word “trigger" in Paragraph 2 probably mean?

A．Cut out.

B．Set off.

C．Slow down.

D．Put off.

2. Which is the main experimental subject in Paragraph 3?

A．Queen bees.

B．Nurse bees.

C．Bee eggs.

D．Baby bees.

3. Why was P. larvae added to the sugar water?

A．To test if it would cause a hive-killing disease.

B．To check how the bacterium would affect the hive.

C．To see whether the target bees would favor the taste.

D．To confirm the bees would pass pathogens to royal jelly.

4. What is the text mainly about?

A．How bees multiply.	B．How antigens function.
C．How bees get vaccinated.	D．How immune system works.