Scientific research shows that animals can show         emotions like human beings. They are sometimes lively, and sometimes bad-tempered.

David got a higher grade in the final exam, for, you see, he made        mistakes.

After the new type of rice was introduced, the farmers produced _______ rice this year as last year. 

—How was your recent trip to Sichuan?—I've never had ________ one before.

The blackboard was wiped _____ .