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