人在生病发烧时,常常没有食欲,原因是( )
A:胃蠕动减慢
B:消化酶催化效率降低
C:心脏跳动加快
D:营养吸收减慢
若直线l1,l2的方向向量分别为V1→=(1,2,3),V2→=(﹣12,﹣1,﹣32),则l1,l2的位置关系是( )
If we spend too much time on the Internet, we won't have enough time to study. , working on computers too long may cause headaches or sore eyes.
-15℃比15℃低30度