1.Do you know what time their plane leave Beijing?
2.I don't feel well today,so I decided to stay at home.
3.The shoes in the shop was quite good.

1.Do you know what time their plane leave Beijing?
把leave改成will leave，一般将来时，根据句子意思，他们的飞机可能还没有离开北京。
由于leave是瞬间动词，还可以用is going to leave，同样是一般将来时。
翻译：你知道他们什么时候离开北京吗？

2.I don't feel well today,so I decided to stay at home.
把decided改成原形decide，前句指的现在，根据句子意思，后面耶应该是现在，所以不能用一般过去时。
翻译：今天我感到不舒服，所以我决定呆在家里。

3.The shoes in the shop was quite good.
把was改成were，shoes是一双，一双是两只，而且shoe用了复数形式shoes,所以动词be应该用are,又因为是一般过去时，are变作were.
翻译：商店里的那双鞋非常好。