“我认为快要下雨了，因为燕子在低飞……不，我敢肯定马上要下雨了！”

因为快要小下雨的时候空气会很湿润小昆虫身上有水蒸气飞的很低所以燕子也飞的低才能抓到吃的啊。

I think it's going to rain soon, because the swallows are flying low...OH!No! I'm sure it's going to rain."

"I think it's going to rain very soon, because the swallow(s) is (are) flying low...No I'm sure it's going to rain."
在此句子里燕子的数量是不明确的,所以如果是单数就需用swallow(燕子)/is,双数就需用swallows(一只以上)/are.
我是在美国长大的,相信我没错的.

”I think it's going to rain in a second, you see, the swallowes are flying in a low height......
No! I bet it's gonging to rain right off!!"

I think soon rained, because swallow in low-flying... I did not dare definitely immediately to have to rain!