211、To be honest, I’m not certain. 212、Maybe. 213、I couldn’t say for sure. 214、I couldn’t say for definite. 215、I couldn’t say absolutely. 216、I’m positive that he did it. 217、I’m certain of it. 218、I’m not sure that’s a good idea. 219、I can’t be certain of what time I left the office. 220、I’ve no idea where my shoes are. 221、I’m not certain if he’s telling the truth. 222、Are you certain this is what you want to do? 223、I swear this is the truth. 224、I have no doubt about how I feel. 225、Absolutely.