English gramma)
Please, can I be explained the rules for these sentences?

1) Yesterday Kate was doing her homework for two hours.

2) Yesterday Kate had been doing her homework for two hours.

Which of two sentences is correct? and why?

Neither is exactly correct. The specific time "yesterday" suggests simple past tense, not a present perfect or past perfect tense. Sentence two could be correct if there were proper context, namely a completed past action that followed it.