Answer:
Step-by-step explanation:
1. Natasha was especially interested in dinosaurs; however, Jorge wanted to check out the huge collection of precious gems.
You need to use a semicolon before however because you are connecting two independent clauses into one compound.
2. Natasha gazed into a replica of a cooking fire and began to imagine sounds: a crying baby, the persistent click of stone on stone involved in making scraping tools, and the thunderous cry of a mastodon.
You need to use a colon to indicate that a list will ensue.