Generally, footprints, scratches, or bite marks left by a predator can reduce an artifact's significance, but when the predator is a famous creature like the T-Rex dinosaur, such markings, known as trace fossils, can be a valuable find for paleontologists.Choice D is the best answer. The convention being tested is coordination of main clauses within a sentence. This choice correctly uses a comma and the coordinating conjunction “but” to join the first main clause (“Generally … significance”) and the second main clause (“when … paleontologists”).
Choice A: It results in a run-on sentence. Two main clauses are fused without punctuation and/or a conjunction.
Choice B: When coordinating two longer main clauses such as these, it is conventional to use a comma before the coordinating conjunction.
Choice C: It results in a comma splice. Without a conjunction following it, a comma cannot be used in this way to join two main clauses.
✨ Expert's Tip ✨
- A period, semicolon, or coordinating conjunction (FANBOYS) can be used to separate complete sentences.
- Keep in mind that two independent clauses cannot be joined by only a comma.