for certain

1.Not obtrusive, go up pertly courtship, you can refuse for certain.

不要莽撞，冒冒失失上去求爱，你肯定会遭拒绝。

2.Miners are a high risk group for certain types of gastric cancer.

矿工是极易患某几种胃癌的高风险群。

3.I don't know for certain.

我并不确切知道。