請閱讀以下短文,然後回答問題。
"If it rains tomorrow, we will cancel the outdoor sports day. Students should bring their homework and stay in the classroom instead."
根據上文,以下哪一句是正確的條件句(conditional sentence)?
It rains tomorrow, we will cancel the outdoor sports day.
If it rains tomorrow, we will cancel the outdoor sports day.
If it will rain tomorrow, we will cancel the outdoor sports day.
If it rained tomorrow, we will cancel the outdoor sports day.