Which of the following statements concerning adverbial clause of time is NOT true?
选项：

A:“When” is often used to talk about an event that takes place at the same time as some longer action or event described in the main clause.
B:“As” can also be used when we want to say that when one thing changes, another thing changes at the same time.
C:In formal speech and writing, we can often leave out “subject + be” in clauses with “when” and “while” if the main and subordinate clause refer to the same subject.
D:“While” is used when you are mentioning a time or event in the past and indicating that a situation has continued from then until now.