18. I am not sure whether I can gain any profit from the investment, so I can’t make a(n) ____ promise to help you.

A. exact B. defined C. definite D. sure

investment 投资

investigate 调查

irrigate 灌溉

irritable 激怒的

navigate 航行

castigate 惩罚

mitigate 缓和，调解，减轻

sure 确信

insure 保险

ensure 确保

define 限定，下定义

final 结束的

refine 提纯

finance 财政，资金