Correct sentences

Hello,

      May I ask which sentences are grammatically correct?

          Is it possible that you be there at 10 o'clock AND

          Is it possible that you are there at 10 o' clock.

          It is important that he be on time AND

          It is important that he is on time.

          It is necessary that he does not see that letter AND

          It is necessary that he not see that letter.

         Thank you very much.

Hi!

For the first sentence, I'd say, "Is it possible for you to be there at 10 o'clock?"

For the second: "It is important that he be on time."

And for the third: "It is necessary that he not see the letter."

Thanks!

Amy