1.The train was full of people, and I had to stand for
over three hours!
火车上全是人,我不得不站了三个多小时!
be full of意为“充满……;装满……”,其后可接可数名词复数或不可数名词。同义短语为be filled with。

Practice
箱子里装满了书。
The box is full ofl filled with books.

2. Well,it's the busiest season in China
because of the Spring Festival.
由于春节,冬季成了中国交通最繁忙的季节。
because of意为“因为;由于”，后可接名词、代词或V-ing形式。例如:
we can't go out for a walk because of the rain.因为下雨,我们不能出去散步。