thE Author thinks thAt thE sErviCE oF thE Bookshop AssistAnt is nEEDED ______.
A．As soon As you EntEr thE shop
B．BEForE you stArt your Browsing
C．only whEn you hAvE FinishED your Browsing
D．AFtEr you hAvE mADE your FinAl DECision