英语语法问题

Question

1, Rare objects are beautifully displayed in glass cases which keep them free from dust.句中为啥不是which are keeping.
2，This being his first visit there, he found a great deal to interest him,句首为啥用being?

Answer 1

1. 不用现在进行时态的原因是因为“物品放在玻璃橱这个状态是一直存在的，不是一会儿就结束了”，所以要用一般现在是时。
2. This being his first visit here, 单看这一部分，可以理解成现在分词短语作this 的定语，但两部分合起来就有问题了，是个病句，建议改成This was his first visit here and he found a great deal to interest himself.