This passage deals mainly with______.
A.the gravitational pull of the Earth and the moon
B.the factors involved in firing a rocket into the outer-space
C.the gravitational fields of the Earth and the moon
D.the speed and direction of a rocket traveling in the outer-space
第1题
梯子如需接长使用,必须有可靠的连接措施,连接后梯梁的强度,不应低于()
A.单梯梯梁强度的90%
B.单梯梯梁强度的80%
C.单梯梯梁强度的70%
D.单梯梯梁的强度
第7题
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