Some of the students are not sure ___ spelling the word, while others are not sure ___ the use of some grammatical rules.
—Is it OK to take this seat?—Sorry, .
-I didn't go to the art show, because I lost my ticket.-You______have borrowed mine I didn't go to see it anyway
Birds'singing is sometimes a warning to other birds________away.
Interest is as_______to learning as the ability to understand,even more so.
I'm pleased to hear that you've come here to _______this matter in person.