You don't have to __________ every new word in the dictionary while reading.
A:look for
B:look up
C:look at
D:look after
显微镜的物镜是40×,要观察640×的物象,应该选用的目镜是( )
羊的白毛和黑毛是一对相对性状.如图是羊的毛色遗传的图解.请据图回答: