1. I like pets very much, but I don't know which one to buy?
我喜欢宠物，但我拿不定主意该买什么？
还能这样说：
I like pets, but I don't know which one is the right one for me.
I am fond of pets, but I am not sure which pet I should buy.
应用解析：
a pet name 昵称；
pet and darling work 得意工作；
pet aversion 第一号讨厌的人或物；
make a pet of 宠爱，把……当宝贝儿
2. What kind of pet do you want?
你想养什么？
还能这样说：
What animal do you want as your pet?
What pet do you want to keep?
谚语：
Kind words are the music of the world.
良言一句三冬暖。
3. How long have you fed your pet?
你养宠物多久了？
还能这样说：
Can you tell me the time you keep your pet?
When did you begin to keep your pet?
谚语：
Well fed, well bred.
衣食足然后知礼仪。
4. What's wrong with the little dog?
小狗怎么了？
还能这样说：
What has happened to the dog?
What is the matter with your dog?
谚语：
Two wrongs don't make a right.
两个错误不等于一个正确。