7

My lucky number is 7, so I always choose it in contests.

用法提示：这里的“7”作为名词，指数字七。

If you add three and four, the result is 7.

用法提示：此句中“7”表示六加一的基数这一含义。

She was excited when she saw 7 on the lottery ticket.

用法提示：这里“7”是名词，作为具体数字出现。