Would you correct my English? ( Dec.13 )

Hello. I wrote two dialogues. Will you correct them?

No. 1

M: Professor Kim, may I have a word [ have a talk ] with you this afternoon?

F: Sure. I don't have class [ I have no class ] at [ during ] the fifth period. About what?

M: I'm writing a paper on global warming. Would you give me some advice?

No. 2

M: What problems do you feel are most important these days [ nowadays ]?

F: Of course, water and food are the most important in the world.

As the population in [ of ] the world increases, they are in short supply.

F: I see. I learned about the population explosion in class.

Thank you. kenta