【题目】It was not until I returned to China this winter after living so long abroad_I began to experience safety and happiness.
A.where
B.before
C.that
D.so

【答案】C
【解析】考查强调句。句意：直到我在海外居住多年之后于今年冬天返回国内时我才开始感受到安全和快乐。此句是一个强调句型，其结构是：It is/was +被强调部分+that/who+句子的其它部分。故选C。