{01}Most parents encourage their children to take an active part in social events, _____ those events do not interfere with their studies. A.concerning B.until C.unless D.provided 解析: 本题选D。
{02}Scientists say it may be five years _____ it is possible to test this medicine on human patients. A.since B.until C.before D.when 解析: 本题选C。
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