--Is your iPad black, Mary?--No, it isn’t. ______________ is white.

There are two dogs in my family. One is white,_____________ black. 

 Even if we are very busy, we should spend ______ doing exercise every day.

I forget to bring a pen. Would you lend me        ?

一I can’t find my pen．Could you lend me ________   ?—Sorry，I’m using it__________．