初中生是未成年人，他们损害国家、集体和他人利益可以不用承担任何责任。[ ]
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______ from the top of the tower, the south foot of the mountain is a sea of trees.
A．Seen
B．Seeing
C．Have seen
D．To see
Not until the early years of the 19th century ________ what heat was.[ ]
A. man did know
B. did man knew
C. didn't man know
D. did man know
