Millions of people around the world suffer from a painful addiction to biting their nails,which can be harder________than smoking cigarettes.
77. --- Have all the important letters been delivered at the first time? --- I’m sorry. _______ only 40% of them.
78. --- You _____ repay this debt this week according to the agreement. --- Don’t worry. I _______ pay it off before the deadline.
79. Ming and Qing tombs have ______ relatively undamaged. They, ______, have suffered some damage from centuries of exposure, wars and deliberate destruction.
80. _______ the right decision _____ the future is probably the most important thing we will ever do in our life.
81. Male and female students are quite different from each other ______ the age at which they begin to develop an intellectual self-discipline.