A possible way to complete these complex sentences is "If you break the rules, you will be punished" and "They found an eerie world while diving".
What is a complex sentence?
This is the combination of an independent clause (complete sentence) and an independent clause (a clause that does not express a complete idea).
How to complete a complex sentence?
In most cases, you need to add either the independent or dependent clause. Based on this, let's complete the sentences:
Sentence 1:
If you break the rules (dependent clause) + you will be punished (independent clause)
Sentence 2:
They found an eerie world (independent clause) + while diving (dependent clause)
Note: This question is incomplete because the options are not given; due to this, I answered it based on general knowledge.
Learn more about dependent clause in: https://brainly.com/question/1838303
