Scientists are learning more about our (67) for sleep. Most people sleep (68) eight hours each night. (69) people sleep more than (70) and others sleep as (71) as two or three hours each night. (72) do not know exactly (73) some people sleep more than others. Dr. Ernest Hartman has an idea about this. He believes the (74) of sleep depends on how a person attacks problems. He said people who need only a few (75) sleep usually are people who have much energy and make good use (76) time to get their work (77) quickly. (78) he said many people who sleep longer than normal de creative work and seem to need (79) dreaming time to find (80) to emotional problems. Some scientists agree with this idea and others dispute.
To determine the (81) of the lack of sleep, scientists have put subjects (82) a set of psychological and performance tests (83) them, for instance, (84) columns of numbers or recall a passage read to them only minutes earlier, "We’ve found that if you’re in sleep deficit (缺乏), performance suffers," says Dr. David. "Short-term memory is (85) , as are abilities to (86) decisions and to concentrate.\
A．And
B．While
C．Thus
D．But
高空A处以水平初速度v0＝
投掷飞镖，在与A点水平距离为
匀速上升，在升空过程中被飞镖击中。飞镖在飞行过程中受到的空气阻力不计，在计算过程中可将飞镖和气球视为质点，已知重力加速度为g。试求：
