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【简答题】
给出下列命题： ① 直线 l 的方向向量为 a ＝(1，－1,2)，直线 m 的方向向量为 b ＝(2,1，－ )，则 l 与 m 垂直． ②直线 l 的方向向量为 a ＝(0,1，－1)，平面 α 的法向量为 n ＝(1，－1，－1)，则 l ⊥ α . ③平面 α 、 β 的法向量分别为 n 1 ＝(0,1,3)， n 2 ＝(1,0,2)，则 α ∥ β . ④平面 α 经过三点 A (1,0，－1)， B (0,1,0)， C (－1,2,0)，向量 n ＝(1， u ， t )是平面 α 的法向量，则 u ＋ t ＝1. 其中真命题的序号是________．
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举一反三
【简答题】根据句意和汉语注释，写出单词的正确形式。 小题1:Parents should have more ______________ (交流) with their children. 小题2:Finally, the climber ______________ (设法完成) to get to the top of the mountain. 小题3:The rich man has a lot ...
【单选题】It can be inferred from the last paragraph that_____.
A.
parents who have babies should be banned from smoking
B.
less smokers regard smoking harmful than nonsmokers do
C.
researchers fail to prove the harm of third-hand smoke now
D.
second-hand smoke does more harm than third-hand smoke
【简答题】以下哪个不属于钢筋常见的连接方式? ( B ) A 、 绑扎搭接 B 、铆钉连接 C 、焊接 D 、机械连接
【简答题】以下哪个不属于钢筋常见的连接方式? ( ) A 、 绑扎搭接 B 、铆钉连接 C 、焊接 D 、机械连接
【单选题】Why did the parents decide they should have fewer children?
A.
So they could give their children a good house to live in.
B.
So they could save some money.
C.
So they could give each one a good life.
D.
So they could have enough food for their children.
【单选题】Parents should pay attention to the cases _______ their children have difficulty adapting to new surroundings.
A.
where
B.
as
C.
why
D.
when
【单选题】Most families in China now have only one child. Parents should teach their children _____ others when they are young. [ ]
A.
what to play with
B.
when to get on with
C.
which to play with
D.
how to get on with
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