Which sentence correctly uses a coordinating conjunction? we listened to the rhythmic sound of the waves as we walked along the beach. the sun peeked from behind the clouds while the gulls flew overhead. shiny seashells dotted the sand; and, i placed one in my pocket. the sandcastle stood far from the tide line, so it was safe from the waves. (not a)

The correct answer is D. The sandcastle stood far from the tide line, so it was safe from the waves.
Coordinating conjunctions, such as AND, SO, etc. connect two or more independent clauses. A is incorrect because AS is a subordinating conjunction and therefore cannot be coordinating. B is incorrect because WHILE is not a coordinating conjunction. C is incorrect even though AND is a coordinating conjunction; however, the sentence is not punctuated correctly (there should be a comma before and and no comma after it).