The entire nation voted on the A) Senate, or B) House in 2018?

Neither. Your poorly written question asked what the "entire" nation did, and not all of the nation can vote.

Those who did vote in 2018, who were not the entire nation, voted on the entire House of Representatives and about 1/3 of the Senate.

House. Only one third of Senate is voted on at a time

I don t answer questions from children.

I wouldn’t base anything on those results. Plus, the entire nation was split.

The entire nation never votes, only those registered voters, i.e., US citizens over the age of 18 who haven't been precluded from voting and who chose to. Now, every state held elections for the Senate and for the House, which are federal, but people who voted voted for both, if applicable, if applicable because Senators' terms are six years and every state only has two, so some states didn't have a senator up for reelection in 2018.

All house sets were up for election in 2018

More people voted for the election of who would go to the House.