a pair of crutches的用法和样例：
- I bought a pair of tan leather shoes the other day.
- He has been crippled since he broke his leg. Now he can't walk without a pair of crutches.
- Billy has a pair of new trousers.
- This small animal has a pair of hazel eyes.
- It has cataloged found items that include an autographed Cubs hat, a large 1921 silver dollar, a pair of crutches, a plastic bag containing $300 in coins and bills, and three digital cameras.