Scientists are learning more about our need for sleep. Most people sleep 【26】______ eight
To determine the 【40】______ of the lack of sleep, scientists have put 【41】______ through a set of psychological and performance tests 【42】______ them, for instance, to add columns of numbers or recite a passage read to them only minutes earlier, "We've found that if you're in sleep 【43】______ , performance suffers," says Dr. David. "Short-term memory is 【44】______ , 【45】______ are abilities to make decisions and to concentrate."
【26】
A.for
B.at
C.in
D.since