生产过程中物料粉碎的目的是什么?
参考答案:
①使物料的表面积增大,提高物理作用的效果和化学反应速度;②促进均匀混合;③提高物料流动性,便于其贮存和输送;④提高产品质量。
Charlie was a rich boy who had more toys than you could imagine. A time came when he was so used to all his toys __________ he began to want something different.
A.as
B.which
C.that
D.when
当一个事务访问某个数据项时,以一定的方式锁住该数据项,从而限制其它事务对该数据项的访问,这种方法称为______。