The correct answer is A. consider.
To consider something is to think about it carefully and weigh up the pros and cons. In this case, the speaker is thinking about whether or not a car is absolutely necessary these days. They are considering the advantages and disadvantages of owning a car, such as the cost, the convenience, and the environmental impact.
The other options are not as accurate. To regard something is to have a particular opinion or attitude towards it. In this case, the speaker is not expressing an opinion, they are simply considering the issue. To think something is to believe it to be true. In this case, the speaker is not stating a belief, they are simply considering the evidence. To agree with something is to accept it as true or valid. In this case, the speaker is not agreeing or disagreeing, they are simply considering the issue.