CSC V1 问题

老师您好， 关于chapter9 order的问题。
S has 10k$ to invest 1k stocks, the current price for the stock is 9$. she is concerning a sudden price increase during he trading day could make the stock getting expensive, what time of order should the client take place?
A. LIMIT ORDER
B. STOP BUY ORDER 
C. A MARKET ORDER 
D. STOP LOSS ORDER
我想请问老师 为什么该题选a？
或者说该怎样区分limit order和stop order呢？这点我并不是很分得清。以我自己的理解，stop order是基于investor对股票走势的预测， 而limit order则有一个specific price
请老师解答 谢谢