Two questions please
My Chinese book wrote this sentence is wrong 你想想才买吧。how can I correct it? Which is correct for this?
你想想就买吧。
你想想再买吧。
My Chinese book wrote this sentence is wrong 他的病还没有好,病好了以后才上课吧how can I correct it? Which is correct for this?
他的病还没有好,病好了以后再上课吧
他的病还没有好,病好了以后就上课吧

Question

Two questions please
My Chinese book wrote this sentence is wrong 你想想才买吧。how can I correct it? Which is correct for this? 
你想想就买吧。
你想想再买吧。
My Chinese book wrote this sentence is wrong 他的病还没有好,病好了以后才上课吧how can I correct it? Which is correct for this? 
他的病还没有好,病好了以后再上课吧
他的病还没有好,病好了以后就上课吧

Answer

再 --> need more time after the action
就 --> do the action immediately 
想 is thinking, you need some time to think before buying
病好了 is getting well, it takes time to get well before having the lesson again

Answer

Why here 再is correct? Why I can't use 就。。。I think （就＆再）can mean ... So why I can't use 就also?

Answer

你想想再买吧
他的病还没有好，病好了以后再上课吧