如图1-57（原图1-60）所示，将粗细均匀、直径相同的均匀棒A和B粘合在一起，并在粘合处用绳悬挂起来，恰好处于水平位置而平衡，如果A的密度是B的两倍，那么A的重力大小是B的_______倍．[5 ]
假设A的长度为x，B的长度为y，横截面积为S，B的密度为ρ，则A的密度为2ρ，有
, 
,
根据力矩平衡条件得
，
代入得 
，
所以
。
本题的正确答案为“”。
Questions 23-30
· You will hear people from the National Food Council complaining to retailers about the high prices they are charging for food products and household goods. They complain that the shops have marked up wholesale prices far too much.
· For each question (23-30), mark one letter (A, B or C) for the correct answer.
· After you have listened once, replay the recording.
The National Food Council has studied A. the reason for selling certain food. B. the supply and demand of certain kinds of food. C. the effect of price increases.