某蛋白质由2条肽链、n个氨基酸组成，该蛋白质至少含有氧原子多少个[ ]
A．n+2
B．n-4
C．n+2
D．n+4
答案：C
Who can ________ a better idea to increase sales?
A．agree with
B．deal with
C．come up with
D．catch up with
