It is generally believed that Watson and Crick’s discovery about DNA was ____ beginning of _____ enormous advances in _____ field of genetics.

been thecomputer for two hours, chatting with a boy from Australia.

It’s seven o’clock now. You must _____ home for school.—OK，mum.

er to look after her sick daughter,the old lady asked for a week’s ________.

Our National Day falls ___ October 1 and thousands of cars pour into freeways ___ the early morning of the holiday.