Answer:
The Electoral Collage is a system that makes us vote for the people in that position to support and hopefully elect the person you were actually voting for. It's a messed up system that makes it so that we don't even vote directly.
This is a compound sentence, because there are two independent clauses here: 1. Stone bridges are strong + but 2. (strong bridges) are costly to build.
The conjunction 'but' connects two independent clauses, and a compound sentence contains at least two independent clauses, whereas a simple sentence has only one.
It is a metaphor and it is like a loud sound, thunder, or lightning, hope I could help
