龈缘线包绕牙冠颈部形成的宽度是（）
A.3～5mm
B.0.5mm
C.2.5～3.0mm
D.6.0mm
E.1.5～2.0mm
参考答案：B
儿茶酚胺是指（）
A.肾上腺素
B.去甲肾上腺素、组胺
C.肾素、多巴胺
D.组胺
E.肾上腺素、去甲肾上腺素、多巴胺
23．In view of lacking preparations for the competition and not wanting to lose face, Johnson eventually decided to _____．
A．drop in
B．drop off
C．drop back
D．drop out
