While 11 stress can be dangerous to the body, short-term stress is actually healthy.
答案：(B) chronic
chronic stress（慢性壓力）與後文 short-term stress（短期壓力）形成對比，表示長期慢性壓力對身體有害，但短期壓力其實有益健康；contagious（傳染性的）、diagnostic（診斷的）、tedious（乏味的）均不符合此處語意。
chronic 這個字，你的印象大概只有醫學上的「慢性病」（chronic disease），一看到它就覺得跟壓力沾不上邊，於是往其他三個看起來比較日常的選項找。但 chronic 的核心意思是「長期持續、拖很久的」，慢性病只是它最常出現的場合，不是它的全部。
四個選項都是形容詞，文法上都修飾得了 stress，可見這一格考的是語意，只能往句子裡找線索。線索就在同一句：While ___ stress can be dangerous to the body, short-term stress is actually healthy. 這裡的 while 是「雖然、然而」，前後兩半要形成對比；後半明明白白寫著 short-term stress，所以空格要的是它的反面，也就是長期的壓力。四個選項裡只有 chronic 站在 short-term 的對立面。
contagious（會傳染的）用在疾病上，壓力不會傳染給別人。diagnostic（診斷用的）講的是用來診斷的工具或方法，不是在說壓力的性質。tedious（冗長乏味的）雖然也帶一點「拖很久」的味道，但重點在無聊，而且全文最後一句才說壓力太少會導致 boredom，方向剛好相反。鑑別度高達 60，分開的正是有沒有把 while 與 short-term 這一組對比讀出來——只看空格附近挑一個跟壓力有關的字，四個都像；讀到對比，答案只剩一個。
chronic（長期的、慢性的）、chronic disease（慢性病）、short-term（短期的）／long-term（長期的）、contagious（會傳染的）、be dangerous to sb（對某人有危險）、while 引導對比子句（雖然、然而）
We all know that too much stress is not good for our health, but too little is not ideal, either. While 11 stress can be dangerous to the body, short-term stress is actually healthy.
Short-term stress triggers the production of protective chemicals in our body and strengthens the body's defenses. 12 our body is in a vulnerable situation, a burst of stress will quickly mobilize the body's own repair system to defend the damaged areas. This 13 us from physical discomfort and sickness.
Small amounts of stress hormones may even sharpen our memory. A recent study found that when rats were forced to swim—an activity that places them under stress for a short while—they remembered their way through mazes far 14 than rats that were in a relaxed state.
The key to a healthy lifestyle is to keep our stress level 15 . Too much stress will make us cranky and sick. Too little stress, on the other hand, will lead to boredom and low motivation.