John and Martha (study) are studying for their upcoming exam. they are in the library now.

i used "are studying" because the action is happening at the present time, "now", i hope its correct :)
Thanks! I am lil bit confused about are and have!
no problem, you are going to use "have" if the verb is in the past participle si
or in the perfect tenses. "have been"
:) hope i helped you