It's very important _______ us ______ every day.
A:for;exercise
B:to;to exercise
C:for;to exercise
D:to;exercise
在一般情况下,如果母亲的卵细胞与父亲的含有X染色体的精子结合,受精卵的性染色体组成就是____ ,由此受精卵发育成的孩子就是____ .如果母亲的卵细胞与父亲的含有Y染色体的精子结合,受精卵的性染色体组成就是____ ,由此受精卵发育成的孩子就是____ .
--I have a cold and my head hurts a lot.
--Oh, sorry to hear that. I hope better soon.