代数式15ax2-15a与10x2+20x+10的公因式是（ ）
A：5（x+1）
B：5a（x+1）
C：5a（x-1）
D：5（x-1）
下列关于新陈代谢的叙述正确的是（ ）
– Mum, I've been studying English since 8 o'clock. _____ I go out and play with Tom for a while?– No, I'm afraid not. Besides, it's raining outside now.
