A:腺嘌呤
B:尿嘧啶
C:鸟嘌呤
D:胞嘧啶
x
…
﹣3
﹣2
﹣1
0
1
y
﹣6
4
6
一Is Amy answering the phone?
一
— _______________ is he?
— He's Peter.