a thing of the past的用法和样例：
- The carefree childhood became a thing of the past.
- Writing letters seems to be a thing of the past.
- Clark once said, "I was born bald!" and indeed his hair was already a thing of the past when he made his screen debut at the age of 33.
- The art of writing letters seems to be a thing of the past.
- The carefree childhood has become a thing of the past.