Researchers have found clear and convincing evidence ________ happiness isthe key to better health and longer lives.

____ skirt is blue.____ is red. Which of them do you prefer?—______ is OK. I like their styles.

Whose backpack is this?— It be Mary’s. She is looking for hers.

Is Mary friend?—No,isn’t.

Can you lend me your bike?— Yes. But you can only ________ it for one day. Because I’ll ride it to school the day after tomorrow.