The beginning of the movie was boring, ________ the end was amazing!
A:but
B:and
C:so
D:or
某班为了奖励在校运会上取得较好成绩的运动员,花了400元钱购买甲,乙两种奖品共30件,其中甲种奖品每件16元,乙种奖品每件12元,求甲、乙两种奖品各买多少件?该问题中,若设购买甲种奖品x件,乙种奖品y件,则可根据题意可列方程组为____ .
化学肥料碳酸氢铵在加热时尤其容易分解,为保存该化肥,通常应采取的措施是( )
38-4=____
63-9=____