28（）
A. When
B. While
C. Since
During
If Keiko can’t adjust to the wild, the foundation （）
A. will set him free anyway
B. will bring him back to the United States
C. will take care of him for the rest of his life
D. won’t be able to take care of him
Why should you know when to stop（）
A. Because you need rest.
Because audience may fall asleep.
C. Because you may be tired for talking too long.
D. Because it can make audience remember what you said.
Stress can affect the respiratory system by（）
A. decreasing the pulse rate
B. a loss of carbon dioxide
C. causing breathing problems
D. causing asthma
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