PART TWO LANGUAGE KNOWLEDGE
SECTION A
Directions: Beneath each of the following sentences there are four choices marked A, B, C, and D. Choose the one answer that best completes the sentence.
21．It was not ______ he took off his dark glasses ______ I realized he was Liu Xiang.
A．when; that          B．until; when    C．when; then    D．until; that