When H7N9 bird flu appeared, people didn't know __________ doctors could cure it.
A:if
B:that
C:what
D:why
1787年美国制宪会议代表们经过激烈讨论,最终放弃立法权为最高权力的早期实践,加强行政、司法权力,行政、立法、司法三权分立制衡。这一变化说明美国( )
计算:(﹣3)×13=____.