因为昨天雨下得很大,所以我们呆在家里.

有好多种句型都可以用呢！
1.The rain was so heavy that we stayed at home yesterday.
2.Because of the heavy rain,we stayed at home yesterday.
3.The heavy rain prevented we go to ___(填因为下雨而不能去的地点)yesterday.
4.The rain was too heavy to we go to ___(同上) yesterday.
5.It was the heavy rain which made we stay at home.(强调句,强调我们呆在家的原因)

Because it rained heavily yesterday, we stayed at home.或
It rained heavily yesterday,so we stayed at home
because和so不能同时用，我们老师讲的

We stayed at home,because it was raining hard yesterday.

It rained heavily yeaterday, so we stayed at home.