Is the sentence “I read a book” present or past tense?
The sentence “I read a book” could be both in present and past simple tense.
The reason is that the past tense of read is read, but we pronounce it (red). So, if you pronounce it (ai ri:d a buk), it is in present simple. If you pronounce it (ai red a buk), it is in past simple.
If we only read the sentence, we should add a time word to show whether the action happens frequently or it happened in the past.
Example: I read a book every day (present simple)
I read a book yesterday (past simple)
You can read more about verb tenses and do some exercises here