81. He walked so fast that I had to run catch up.
82. We did not have enough time to study this plan in detail yesterday.
83. Scientists are looking for ways to solve this problem.
84. They finished the task ahead of time, although there were many difficulties.
85. Jack waved to his friends until the train disappeared in sight.
86. Studients all worked hard at their study, so everyone of them passed the exam.
87. She found herself fall in love with him over time.
88.Nobody talked about it before I spoke of the accident.
89. Not all the members attended the meeting yesterday.
90. We'd better put off the outing since so many students cannot come.