Question

If the -ing form of a verb is used as the main verb of the predicate, the auxiliary must contain a form of

1) be
2) do
3) have
4) will
5) none of these

Answer 1

Its Be.
Here let me show you why.
I will BE doing, She will BE sleeping. Sounds correct.
I will do sleeping, she will do walking. Nope. Sounds wrong.
I will have sleeping : nopee.
I will sleeping no.
So the correct answer is BE