—Must I turn off the gas after cooking ? --Of course . You can never be ___ careful with that.

To understand the grammar of the sentence, you must break it       into parts. 

I must go now. _____, if you want that book I'll bring it next time.

Although ____ my opinion, the old professor didn’t come up with his own.

 It’s hard for him playing against me. I’ve got nothing to play for, but for him, he needs to win so __________.