根据句意，用括号内所给单词的适当形式填空。
It is clear that most of the ___________ (tourist) bags are full of souvenirs.
After a night’s work without sleep, he looked very ___________ ( sleep).
More and more people have realized the ___________ (important) of wetlands.
The old man looked __________ (sad) at his grandson with tears in his eyes.