根据句意及汉语提示，写出各单词的正确形式，每空一词。

1．Simon and Linda asked each other to keep their secret to _________（他们自己）．

2．It's so _________（不公平的）!Mary gets more money for less work．

3．Several American visitors watched the raising of the national _________（旗帜）in our school last Monday．

4．We thought the river was too wide for Andy to swim _________（穿过）．Luckily，he did it successfully．

5．The snow is _________（厚的）today than yesterday．What about playing with snow outside?