1 . Directions: Fill in each blank with a proper word chosen from the box. Each word can only be used once. Note that there is one word more than you need.

A. content B. demands   C. guard     D. depressed   E. prioritized   F. fits G. failure   H. meant   I. competed     J. mere     K. independent

Happiness, as the Brazilian poet Vinicius de Moracs put it, is “like a feather flying in the air. It flies light, but not for very long.”

Humans are not designed to be happy or even     1    . Instead, we are designed primarily to survive and reproduce, like every other creature in the natural world. A state of contentment is discouraged by nature because it would lower your     2     against possible threats to your survival.

Evolution has     3     the development of a big frontal lobe(脑叶)in our brain (which gives us excellent executive and analytical abilities) over a natural ability to be happy. Different geographical locations and circuits in the brain are each associated with certain neurological(神经系统的)and intellectual functions, but happiness, being a(n)     4     idea with no neurological basis, cannot be found in the brain tissue.

In fact, experts in this field argue that nature’s     5     to eliminate depression in the evolutionary process is due precisely to the fact that depression as an adaption plays a useful role in times of difficulty, by helping the     6     individual get away from risky and hopeless situations in which he or she cannot win.

Our emotions are mixed and at times contradictory, like everything else in our lives. Research has shown that positive and negative emotions can coexist in the brain relatively     7     of each other. This models show that the right hemisphere processes negative emotions preferentially, whereas positive emotions are dealt with by the left-sided brain.

It’s worth remembering, then, that we are not designed to be consistently happy. Instead, we are designed to survive and reproduce. These are difficult tasks, so we are     8     to struggle, seek safety, fight off threats and avoid pain. The model of competing emotions offered by coexisting pleasure and pain     9     our reality much better than the unachievable bliss(极乐)that the happiness industry is trying to sell us. In fact, pretending that any degree of pain is abnormal will only develop feelings of inadequacy and frustration.

So, if you are unhappy at times, this is not a shortcoming that     10     urgent repair. Far from it. This fluctuation(波动)is, in fact, what makes you human.