Maybe you should __________.
A:call on her
B:call him at
C:call him up
D:call up her
我国科学工作者培育的转基因抗虫棉,其抗虫基因来源于 ( )
工人师傅在用方砖铺地时,常常打两个木桩,然后沿着拉紧的线铺砖,这样地砖就铺得整齐,这个事实说明的原理是____