What was the purpose of the party-nominating conventions, which were started during the jacksonian era?

to give more people a say in choosing candidates
to present new techniques for promoting candidates
to debate important economic and political issues
to increase the voting rights of the common people
to address problems faced by american indians

The best answer for this question would be:

to increase the voting rights of the common people

Andrew Jackson had experienced broken politics at the time of their elections. He was against a candidate that had the same  objectives and mission like him and yet he had won because of the House of Representatives that voted. The Jacksonian era, was a time wherein the voting rights had to be changed, for people to have the freedom of opinion in order to vote wisely. Andrew Jackson saw how unfair the political system was and wanted to change how it was suppose to be. He thought right that it was the people' chose.