请教二道语法题, 0008, 36, 38. 谢谢

36. The nectar of flowers (are ingested) by worker bees and (converted) to honey in (special) sacs in (their)digestive systems.
A B C D
答案是D, 可我就是不明白,为什么? 不是be done by 吗?

每次一出现这类的题我范湖了.

又加了一道

38. The (sensation) of (sound) is produced (how) vibrations transmitted through the air (strike) the eardrum.

答案是D, 不明白为什么

谢谢了

36题答案应该是A吧？nectar是不可数名词，谓语动词怎么能用复数？

38题答案是C。The sensation of sound is produced 是完整的主句，应该把how改为when引导状语从句。