题干
I'm _____, and I have a _____sister.
A：15 year old, 16-year-old
B：15 years old, 16-years-old
C：15-year-old, 16 years old
D：15 years old, 16-year-old
答案(点此获取答案解析）
D
）混合后脱水生成二肽，其二肽种类最多为