Can I say "contestar las preguntas" instead of "contestar a las preguntas"?

Question

In my spanish text book there is a sentence:

¿Tenéis que contestar a las preguntas de la profesora?

Since "contestar" can be followed directly by objects, why should we use a preposition "a" before the object here?

Can I just say:

¿Tenéis que contestar las preguntas de la profesora?

Answer 1

Yes, both phrases are equally valid, though most people I know usually omit the "a."