C'est l'ex 2 je ne comprend pas on doit compléter avec l'auxiliaire BE

a)What is that noise . What is the dog doing ?
 b)Jim?? Are you playing on your computer? 
 c)No mum we are not playing , we are ...
 d)They  are building a new post office..
 e)You are not going to the party because...
 f) Is Sarah leaving London in June ? yes she is