As I was walking along the beach ,I noticed a fishing boat _

As I was walking along the beach ,I noticed a fishing boat _______(sink)
为什么要用sinking而不是were sinking
->因为前面有notice,notice doing 注意到渔船正在沉 其实用was sinking也可以,只是没有前面那个好
Then I smelt something ____(burn)为什么用burning而不是were burning
闻到有个东西正在烧 doing 强调连续性和进行性,根据句意“我闻到某东西正在燃烧”,很明显burning.
and saw smoke 【coming】 under the door
come表示出来