1）用於表示在時間的某壹點或某壹時刻。例如:
What were you doing at this time yesterday?
Students often start classes at eight o'clock in the morning.
2）用於表示在三餐或中午、晚上。例如:
What did your mother say at breakfast ／lunch ／supper time?
We heard a girl singing in the next room at noon ／night.
3）用於表示節氣、年齡。例如:
Children often receive presents at Spring Festival.
Jim began to play the piano at the age of seven.
2. in
1）用於表示在壹段時間內。例如:
Mother will be back in a few days.
2）用於表示在非特指的早晨、上／下午、夜晚。例如:
My English teacher often gets up before 6o'clock in the morning.
My grandparents like watching TV in the evening.
3）用於表示月份、季節、年、世紀等。例如:
I was born in February, 1963.
Everything begins to grow in spring.
The Olympic Games will be held in Beijing in 2008.
The story happened in the 20th century.
3. on
1）用於表示在具體某天或某壹特定日子的上午、下午或晚上。例如:
His mother was born on January 18, 1956.
She often does her homework on Saturday afternoon.
The old man died in the mountain on a cold winter afternoon.
2）用於表示節日。例如:
Children often go to church on Christmas Day.
People visit their relatives and friends on New Year's Day.
但是在含有early morning, late afternoon之類的詞語時, 通常用in, 而不用on。例如:
in the early morning of 21st, March;
in the late afternoon of 15th, September
另外, 由last, next, this, that, these, those等詞構成的表示時間的短語前面, 通常不用任何介詞。yesterday, today, tomorrow, tonight等詞前面也通常不用介詞。例如:
He bought a Chinese-English dictionary this morning.
They traveled to Beijing last summer.
You'd better finish your homework tonight.