1. Read the text below. Choose from A to D to complete the gaps 1-5
2. Explain your choices from the point of grammar

The correct choice here is B. used to be. This phrase indicates a past habitual action or a state that existed before, which fits well with the context of sibling rivalry that existed before psychologists began to understand it.

The suitable choice is C. realistic. This word is needed to complete the sentence grammatically. "But in realistic what can parents do..." - it's asking about what practical steps parents can take in reality to prevent similar occurrences.

The appropriate choice is D. By the time. This phrase is used to indicate a point in the past when something had already happened, which fits the context of comparing the achievements of siblings at specific points in time.

The correct choice is A. had been reading. This choice matches the structure required for the past perfect continuous tense indicating an action that was ongoing in the past up to a certain point.

The right choice here is D. were doing. This choice fits in the context of the sentence, highlighting that the parents were unaware they were causing harm through their actions. The phrase "they were doing any harm" denotes an ongoing action in the past.