Распространенные ошибки
Can changes to could in subordinate clauses, when the verb in the main clause is in the past simple tense.
When the verb in the main clause is in the past tense, use a past tense in subordinate clauses.
This rule doesn't apply (1) to verbs within quotations, (2) to facts that are true at all times. We say:
1. She said, 'I am waiting for your answer'
2. He said that London is a great city
If you begin with a verb referring to past time, keep the verb forms in the past. The same rule applies to tenses throughout a composition.
Will changes to would in subordinate causes, when the verb in the main clause is in a past tense.
Use the simple past tense (and not the present perfect) for an action complete in the past at a stated time.
When a sentence has a word or a phrase denoting past time, like yesterday, last night, last week, last year, then, ago, etc., always use a simple past tense.