Answer:
The first question has two correct options (sentences).
B. After noticing his cleat was untied, the runner stopped to tie his laces.
C. Stopping to tie his laces, the runner forfeited his first-place finish.
Second question:
The closest correct option is C.
But, in fact the sentence "Selected for a national baking show, Mariana was ecstatic, and she planned to create the best cake of her life to win the grand prize." has three clauses (two independent and one dependent), so it is a compound-complex sentence.
Step-by-step explanation:
First Question:
Complex Sentences:
Complex sentence have one independent clause with at least one dependent clause.
Independent clause has a subject and a predicate (a verb and stating something about the subject) AND it can stand alone as a sentence (expresses complete thought/idea.
A dependent clause has a subject and a verb AND it does not express a complete thought.
Examples:
Although he was busy (dependent), he listened to her patiently (independent).
He could not attend the class (independent) because he was sick (dependent).
Second Question:
Compound Sentences:
Compound sentences have two independent clauses which are joined together by a comma AND a coordinator (for, and, nor, but, or, yet, so - FANBOYS) or they are joined just by semicolon (no coordinator).
Examples:
He has all the money of the world, yet he was sad.
Some people prefer to stay home on Sundays; others go outdoors.
Compound-Complex Sentences:
These sentences have at least two independent clauses and a dependent clause.
Example:
The final ended in a tie (independent), so every one was happy (independent), because they shared the honors (dependent).