Incorrect: He asked had we taken our food.
Correct: He asked if / whether we had taken our food.

Explanation
We use a conjunction like if or whether to introduce indirect yes/no questions. Note that indirect questions have the same word order as assertive sentences – that is, the subject comes before the verb.

Incorrect: She asked him what was he doing.
Correct: She asked him what he was doing.

Incorrect: John asked to Peter why their father is angry.
Correct: John asked Peter why their father was angry.

Explanation
When the main clause is in the past tense, the subordinate clause will also be in the past tense.

Incorrect: He asked that what am I doing.
Correct: He asked what I was doing.

Incorrect: He does not care for my words.
Correct: He pays no attention to what I say.
Incorrect: No one cared for the children after their mother died.
Correct: No one took care of the children after their mother died.
Incorrect: He does not care for money.
Correct: He does not take care of his money.

Explanation
The misuse of care for is very common and the sentences given above need practice.

Incorrect: When we went there we found that the lion was disappeared.
Correct: When we went there we found that the lion had disappeared.
Incorrect: He said that his father died last year.
Correct: He said that his father had died last year.
Incorrect: I did not see him because he went out before I arrived.
Correct: I did not see him because he had gone out before I arrived.
Incorrect: He got angry before I said a word.
Correct: He got angry before I had said a word.
Incorrect: I met a man who was my classmate 20 years ago.
Correct: I met a man who had been my classmate 20 years ago.

Explanation
The sentences given above are the examples of the common failure to use the past perfect tense when the time of one past tense verb is more past than that of another.