Answer:
D) for this reason
Explanation:
The sentence shown in the above question shows two statements that maintain a cause / effect relationship. That is, the phrase shows why car manufacturers began installing factory-installed car seats, the reason was the cases of severely injured children. For this reason, we can say that the correct option to complete the blank space is "for this reason", so the sentence would look like this:
Children can be seriously injured if not properly restrained in a vehicle; for this reason many car makers have begun installing factory installed car seats.
