In a Han Dynasty tomb, they found some precious jars and vases, _______ are valuable

Jack can’t concentrate on his lessons recently.— Yes, that might ____ why he did so badly in the last test. [ ]

The desk is ________ heavy ________ carry.

When I turned to the person ________ next to me, I recognized that he was my schoolmate[ ]

Which is _______ from the sun, the moon or the earth