SC让我郁闷到要死掉

都是SC大全上的题目：

1。After a few weeks’ experience, apprentice jewelers can usually begin to discriminate, though not with absolute certainty, genuine diamonds from imitation diamonds.
(A) genuine diamonds from imitation diamonds
(B) genuine diamonds apart from imitations
(C) between genuine diamonds and imitation diamonds
(D) among genuine diamonds and imitation diamonds
(E) whether diamonds are imitation or genuine
我选A，答案却是C。查了字典，字典里明明白白写着词的用法：discriminate between A and B; discriminate A from B. 还有例句：discriminate between two cases, discriminate one case from another。怎么看A都更符合标准用法啊。这两个到底有什么区别啊？请高人指点。

同样的还有DIFFERENTIATE AND/FROM，这个到底有什么区别呢？

2。Most North Carolina ski resorts broadcast music onto the slopes; skiers can choose among hard rock, soft pop, and “beautiful music” slopes, there are no slopes without music.
(A) skiers can choose among hard rock, soft pop, and “beautiful music” slopes, there are
(B) because skiers can choose hard rock, soft pop, or “beautiful music,” there are
(C) however, skiers can choose among hard rock, soft pop, “beautiful music,” and
(D) although skiers can choose among hard rock, soft pop, and “beautiful music” slopes, there are
(E) skiers can choose among hard rock, soft pop, “beautiful music” slopes, but
我选了B，答案却是D。这个ALTHOUGH到底是表达什么呢，怎么读都没有让步语气的意思啊。虽然CHOOSE A，B，OR C里的这个OR有点AWKWARD，但GMAT不是强调逻辑意思吗？ALTHOUGH表达怎样的逻辑意思呢？