单选题 He opened the door and let himself in quietly ______ not to wake the family.
【正确答案】 B
【答案解析】[解析] 他为了不吵醒家人，打开门悄悄地进来了。
本题考查连词的用法。so as to为了。because后面跟原因状语从句；so that后面跟目的或结果状语从句。故选B。