题干
The doctor is very __________ about what to eat and never eats fast food.
A：especial
B：special
C：unusual
D：particular
答案(点此获取答案解析）
D
（a、b分别代表不同的原子或原子团）互为同分异构体。据此推断一氯丙烯的同分异构体（不含环状结构）共有 （ ）