铆钉有半圆头铆钉、平头铆钉和抽心铆钉等, 用于金属板材与材料, 风管和部件之间的连接。垫圈有平垫圈和弹簧垫圈, 用于保护连接件表面免遭螺母擦伤, 防止连接件( )。
A. 紧固
B. 防潮
C. 严密
D. 松动
【单选题】Which is the largest organ of human body?
A. stomach
B. skin
C. rectum
D. heart
【单选题】Which one of the following is NOT a function of skin?
A. protection
B. regulation
C. sensation
D. ventilation
【单选题】Which one of the followings is NOT a natural solution of hives?
A. acupuncture
B. oatmeal bath
C. coconut oil
D. aloe vera lotion