political parties hold national party conventions mainly for the purpose of

a. choosing electors for the electoral college
b. selecting a presidential candidate
c. approving the party platform
d. selecting party candidates for Congress

Is it B?

I agree.

Yes, you are correct. Political parties hold national conventions primarily for the purpose of selecting a presidential candidate. During these conventions, party delegates from across the country gather to officially nominate their party's presidential candidate for the upcoming general election. The candidate is usually chosen through a series of delegate votes and sometimes involves speeches, debates, and other forms of campaigning. Additionally, national party conventions also serve as a platform to showcase the party's values, promote party unity, and generate enthusiasm among party members and supporters leading up to the general election.