以下是朗文Advanced Part5的两道问题，希望高手不吝赐教
TRANSITION WORDS
3. The ads can bring in revenue;___,because they are government
sponsored,they can keep our costs to a minimum.
(A)for example (C)moreover
想问:答案(C)moreover，但是用(A)for example
这广告带来收益，举例来说，因为政府的补助，所以他们花费最少.
用for example来表示为什么有收益，并举例理由，这种文法不行吗？
COORDINATE CONJUNCTIONS
10Lee took the brochures to the printer's last Friday,
___Tina picked them up early this morning.
(A)and (C)so
想问:答案(C)so，但是用(A)and
李上礼拜五拿手册去打印，所以Tina今天早上将它们给拿回来.
这样文意好像也没有问题，为什么不能用SO？