Student or Learner
The underlined are the answers to my grammar book's excercise questions, and they specify only past perfect, which mean the contrary of past events. But can't they be also be replaced with past tense like "took" and "didn't meet", which denote the opposite of the present?
Don't they also make sense logically?
3. If she had taken my advice, she wouldn't be in trouble now. =>took
4. If we hadn't met each other, what would you do(be doing) now? =? didn't meet
In each case the tense chosen by your book makes it clear that the conditional action occurred before the main action. In the other cases the relative times are unspecified. That is why the past perfect is better. In fact, that is why the past perfect tense exists.