材料在建筑物上所受到的力有（）
A、拉力
B、重力
C、压力
D、弯曲
E、剪力
参考答案：A, C, D, E
Aunt Li often asks her son ______ too much meat. It's bad for his health. [ ]
A. don't eat
B. not to eat
C. not eat
D. to not eat
免疫的核心问题是（）
A.识别“自身”与非“自身”
B.对自身物质产生耐受
C.抵御细菌.病毒感染
D.抵抗肿瘤
