Question

-------------，we decided to leave at once,as we didn't want to risk missing the bus.

A, As it being pretty late B, It being pretty late C, It was being pretty late D, Being pretty late 为什么选D?希望能说的详细点！

Answer 1

每个句子只能有一个主句！在这个原则的基础上，因we decided to leave at once主谓齐全，所以可以确定，空格部分需要的是状语成分，A和B，形式错误，排除！C，为主系表结构，是个完整的句子，不可和we decided to leave at once同时存在于一个句子中，所以排除。D为原因状语，形式内容皆可。选D.

Answer 2

现在分词作原因状语，所以用being
pretty
late，其他选项都出现了另一个主语，所以不能选

Answer 3

选D, 原因状语从句.原局是 It was pretty late,.........................

Answer 4

Being pretty late 现在分词做状语，表“迟到”这个状态。分词与句子主语为主谓关系，表示与谓语动词同时发生或基本同时发生。以上句子中他们很迟了，即决定马上出发。
又：Being asked to sing a song for them, she couldn’t very well refuse.