根據(jù)句意及漢語提示，寫出各單詞的正確形式，每空一詞。

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

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 _________（旗幟）in our school last Monday．

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

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