56.He tried to repair the engine, but without____ (succeed).
57. I said goodbye to them with a mixture of____ (sad) and joy.
58. There was a____ (drama) increase in the world population in the first half of the 20th century.
59. Good teamwork is a____ (power)tool for effective management.
60. There have been great advances in the____ (treat) of cancer.
61. When I was at school, we were required to ____ (memory) a poem every week.
62. The Internet provides many resources that were previously____ (available) to us
63. College was more difficult than he had expected; however, he managed to reach his____ (origin) goals.
64. This photo is too small. Please____ ____ (large) it for me.
65. For your ____ (safe), we advise you to keep your seat belt fastened during the flight.