I really don’t know _____ I put my wallet after I paid the bill

The two girls are so alike that strangers find _____ difficult to tell one from the other. [ ]

It has been proved ________ eating vegetables in childhood helps to protect you against serious illnesses in later life[ ]

Yao Ming, who ______ the Houston Rockets, is working hard to make his dream come true

The farm ______ we see today is no longer the one ______ it was ten years ago.