生活中的下列物质中,属于纯净物的是 [ ]
A.酱油
B.管道煤气
C.食醋
D.蒸馏水
答案:D
一位母亲记录了儿子3—9岁的身高,数据(略),由此建立的身高与年龄的回归模型为y=7.19x+73.93,用这个模型预测这个孩子10岁时的身高,则正确的叙述是
A.身高一定是145.83cm
B.身高在145.83cm以上
C.身高在145.83cm左右
D.身高在145.83cm以下
The boy said ________ couldn't he work out the problem but his teacher didn't know how to do it.
A.though
B.never
C.hardly
D.not only