Look at the trouble I am in! _______I had followed your advice.

A．Only if

B．If only

C．Even if

D．So long as

步骤3

A．4秒后放开推动活塞的手指
B．助手用拇、示两指卡紧皮下环处的输精管，术者卡紧皮肤针孔前方的输精管
C．用盛有4ml空气的注射器，接在已穿入的针座上
D．回抽无血液后，将活塞推至2ml刻度处
E．若穿刺成功，活塞则因内压关系自动退回到原该刻度