In sentences like “It is going to snow”, the subject “It” ______

In sentences like “It is going to snow”, the subject “It” ______.
A、is not the unseen all-powerful force of nature
B、is not a conceptual habit of the speaker
C、a grammatical requirement of the linguistic system
D、All of the above
【正确答案】：D
【题目解析】：In sentences like “It is going to snow”, the subject “It” is not the unseen all-powerful force of nature, nor is it a conceptual habit of the speaker, but merely a grammatical requirement of the linguistic system.