单项选择题

阅读下面的短文，文中有15处空白，每处空白给出了4个选项，请根据短文的内容从4个选项中选择1个最佳答案。
Making the Leap Jumps play a big role in many styles of dancing. Generally, what makes a jump impressive is its hang time, the amount of time a dancer spends in the air. The quest for greater hang time is a battle against gravity, the constant (1) pull of Earth, said Laws. To leave the ground at all, a dancer has to use leg muscles to create an upward push that is greater than Earth’s downward pull. But the final (2) of any jump depends on just one thing: the upward speed of the body just as the dancer leaves the ground. Strengthening muscles so they can push harder is one obvious (3) to achieve higher jumps and increase hang time. But ballet dancers also use a simple trick to gain the illusion of staying in the air longer without actually doing so. In a huge sideways jump called a grand jete, a (4) ballet dancer seems to float for an impossible length of time. Of course, a dancer can’t really hang in the air. The laws of physics decree that during any jump, a dancer’s center of gravity must follow a parabola. A parabola is the same (5) path a ball takes when you throw it into the air. So how do dancers make it look like they’re hanging in the air A dancer (6) the illusion of floating in the air by lifting her legs and arms as she approaches the peak of the jump. The (7) of her body — her torso and her head — respond by sinking a bit. If her timing is just right, she’ll seem to float sideways, instead of rising and falling. The effect is not only beautiful; it (8) makes the jump seem bigger by "stretching out" the peak. Of course, what goes up must come down. During a typical grand jete, a dancer’s center of gravity rises 2 feet (9) the ground. Pulled by gravity from such a height, the dancer’s body falls very fast —roughly 3.4 meters per second —by the time it reaches the floor. As it falls, the body carries with it momentum. Momentum is the weight of the body multiplied by its (10) The bigger the body is and the faster it falls, the greater its momentum. The only way a dancer can stop dropping through the air is by stopping the body’s momentum, which requires an (11) force from the ground. Landing can be very jarring to a dancer and can (12) injuries. The dancer call ease the landing by bending her knees and letting her aims fall, but she also gets help from an unexpected source: the floor. Wooden dance floors are designed to act (13) shock absorbers. They are spring’y and can recoil as much as an inch under extreme pressure. That little bit of give makes a big (14) Landing on a springy floor, the dancer undergoes a slower change in momentum than she would hitting a rigid floor. The give in the floor allows the decrease in momentum to happen more (15) with less force and less chance of injury. jete n. (芭蕾舞中的)小跳 jarring adj. (产生)反弹力的 decree v.规定 springy adj.有弹性 parabola n. 抛物线 recoil v. 后缩 torso n.躯干 give n. 弹性，可弯性 momentum n.动量 1. A. parallelly B. upward 2. A. center B. height 3. A. street B. road 4. A. skillful B. beautiful 5. A. smooth B. short 6. A. changes B. uses 7. A. force B. movement 8. A. too B. also C. yet D. so 9. A. off B. out of C. along D. onto 10. A. temperature B. speed C. moisture D. time 11. A. rising B. falling C. opposing D. responding 12. A. increase B. cure C. remove D. cause 13. A. like B. love C. protect D. cancel 14. A. sameness B. resemblance C. difference D. nearness 15.

A. gradually	B. strongly
C. spontaneously	D. incidentally