1] The law cannot become the guardian of our private manners. (Use- Be unable to)

Ans: The law is unable to become the guardian of our private manners.

2] I couldn’t pay the fare. (Use- Be able to)

Ans: I was not able to pay the fare.

3] We cannot get them back by invoking the law. (Use- Be able to)

Ans: We are not able to get them back by invoking the law.

4] He could not rest till he left it behind a couple of hundred miles. (Use- Be unable to)

Ans: He was unable to rest till he left it behind a couple of hundred miles.

5] But no legal system could attempt to legislate against bad manners. (Use- Be able to)

Ans:  But no legal system was able to attempt to legislate against bad manners.

6] Wordsworth was able to gather lessons of wisdom. (Remove -Be able to)

Ans:  Wordsworth could gather lessons of wisdom.

7] How can you be otherwise with Saturn where he is? (Use- Be able to)

Ans: How are you able to be otherwise with Saturn where he is?

8] If only he could reach a table in the restaurant unsuspected, success would be his. (Remove - could)

Ans: If only he was able to reach a table in the restaurant unsuspected, success would be his.

9] The king is able to do nothing wrong. (Remove - Be able to)

Ans: The king can do nothing wrong.

10] She was able to face the whole horror. (Remove - Be able to)

Ans:  She could face the whole horror.

Examples:

11] she could not be fashionable. (Remove - Be able to)

12] You can’t get out of it now. (Use - Be able to)

13] Now she could see flies crawling slowly out of a saucer of milk with their wings stuck together. (Use - Be able to)

14]I  can  buy  some  jaggery  and  coconut tomorrow. (Use - Be able to)

15] can imagine that lift-man, (Use - Be able to)

16] he can have the service for asking(Use - Be able to)

17] It cannot be too widely diffused (spread) in a rather drab (gloomy) world. (Use - Be able to)

18] We cannot get them back by invoking  the law. (Use - Be able to)

19] you can also track the condition of the goods. (Use - Be able to)

20] Why can’t we produce good toys in India?  (Use - Be able to)