?每天是指每隔24小時的一段時間，通常用來表示日常的、重復發生的或者習慣性的事情。它可以作為一個名詞或者副詞使用。

作為名詞時，every day可以指代一天中的所有時間，也可以指代某個特定的日期。：

1. I go to the gym every day. (我每天都去健身房。)

2. Every day is a new opportunity to learn. (每一天都是學習的新機會。)

3. I have been working on this project every day since last month. (自從上個月以來，我每天都在這個項目上工作。)

作為副詞時，every day通常放在動詞之后，用來修飾動作發生的頻率。：

1. She brushes her teeth every day. (她每天都刷牙。)

2. The children play in the park every day after school. (孩子們放學后每天都在公園里玩耍。)

3. He checks his email every day before going to bed. (他睡覺前每天都會查看郵件。)

除了表示日常習慣外，every day還可以用來表示連續不間斷的時間段，通常與for連用。：

1. The restaurant has been open for business every day for the past 10 years. (這家餐廳過去10年里每天都營業。)

2. She has been studying English for two hours every day. (她每天都學習英語兩個小時。)

此外，every day也可以用來表示平均值或者頻率。：

1. The temperature is around 25 degrees every day in summer. (夏天每天的氣溫大約在25度左右。)

2. On average, she receives 50 emails every day. (平均來說，她每天收到50封郵件。)

總的來說，every day是一個常用的詞組，可以用來描述日常生活中發生的事情，也可以用來表示時間段、頻率或者平均值。它的使用范圍很廣泛，在口語和書面語中都可以使用。

例句參考：

1. I try to exercise every day, but sometimes I just don't have the time.

(我盡量每天都鍛煉，但有時候就是沒有時間。)

2. The sun rises and sets every day, it's a natural cycle.

(太陽每天升起和落下，這是一個自然循環。)

3. He has been traveling for months and hasn't been home every day since then.

(自從幾個月前開始旅行以來，他每天都不在家里。)

4. She practices the piano for an hour every day, and her skills have improved significantly.

(她每天練習一小時鋼琴，她的技巧有了顯著提高。)

5. The store is open from 9 am to 9 pm every day of the week.

(這家商店每天從早上9點到晚上9點都營業。)