This question is so hard that very ______ students can answer it.

—You see, “Food Safety” receives thousands of Internet hits a day.—Obviously, it has become one of the _________ topics recently.

Ann is a ______ girl because she often leaves books in the park.

This book is  ________for a six-year-old child to read.

Mobile phones are very popular in China now and they are ______ than before.