A:因三角板中间是空的,所以没有确定的重心
B:在挖空部分的中心
C:在某个角的顶点
D:在某条边的中点
读“沿我国32°N地形剖面示意图”,回答下列问题.
在正方体ABCD﹣A1B1C1D1中,下列各式中运算的结果与向量 AC1→ 共线的有( )
①( AB→ + BC→ )+ CC1→ ;
②( AA1→ + A1D1→ )+ D1C→1 ;
③( AB→ + BB1→ )+ B1C1→ ;
④( AA1→ + A1B1→ )+ B1C1→ .
My name is Sally. I am a school girl. My school is far from my home. So I can't go to school by bike. I often go there by bus. I must get up very early every morning. I have no time for breakfast at home. I often eat something for breakfast on the way(在路上). I want to go to school on time(按时).
下列关于植被类型的叙述,错误的是( )
考古发掘的一只汉代漆杯,其底部刻有六位不同工种工匠和七位监督人员的名字。这反映了当时中国的官营手工业( )