Which best describes one of a senator's roles as a lawmaker?

One function of the senator is to integrate senate committees, which may be temporary or permanent. These are the environments in the legislative house in which specific problems are discussed - such as economics, agriculture, security - and where there is a deeper debate around bills, constitutional amendments, etc.

In the Senate, the functions can be legislative, fiscalizing, authorizing, judging, approving authorities, among several other competences.

serving on a committee