1 They sailed along _ Yellow River for two weeks before they

1 They sailed along _ Yellow River for two weeks before they arrived _ home.A the ,/ B the,the 答案写的是B 应该选A吧?
请指教,
2 Some girls get sick after they try so hard to lose_weight.
A a B an C the D /
不过应该是D吧?loose weight 不是减肥的固定词组吗?请指教～说明理由～
3 It is known to all that _light travels faster than _ sound.
A /,/ B a,a C the ,the D the ,/
,不过light 和 sound 不都是不可数吗?而且这里泛指,应该是A吧?请指教～
我没搞错，书里的答案的确印错了。还不如不看答案呢。我可以相信自己吧。嘻嘻。