人的头部被头发覆盖的面积约为254cm2，若每平方厘米上长有头发140根，试用科学计数法表示一个人的头发的总量。
解：140×254=3.556×104。
阅读理解，选择正确答案。
Jim and Mary are brother and sister. They are twins. They like to swim and ride a bike. They like to fiy
kites, too. They often fly kites near the river. The kites are very high. They are very happy. But not all of their
favourite games are the same. Jim likes to play soccer and Mary likes to play ping-pong. Jim likes to jump high.
He thinks it's easy. But Mary thinks it's very hard. Mary likes to play with doll, but Jim doesn't. Mary can sing
very well and Jim can throw yo-yo very well.
l. They both like .[ ]
A. swimming
B. riding a bike
C. flying kites
D. all of them
2. Where do they often fly kites ?[ ]
A. Near the river.
B. On a hill.
C. Near their houses.
D. At school.
3. What game does Mary like ?[ ]
A. Soccer.
B. Basketball.
C. Ping-pong.
D. Volleyball.
4. What game does Jim like ?[ ]
如图，跳水运动员在入水过程中，身体所受的浮力__________(选填“增大”、“减小”或“不变”)， 受到水的压强_____________(选填“增大”、“减小”或“不变”)，若跳水池水深5m，则水池底面受到水的压强是____________Pa。（g取10N/kg）
