Correct Answer: D
Explanation:
A comma cannot be used by itself to join two independent clauses, so "substance, it" contains this sentence's error. The first independent clause in this sentence is "Baking soda, also known as sodium bicarbonate, is a truly useful substance." The second independent clause is "It can be used for cooking, baking, and cleaning." Two independent clauses can be joined into a compound sentence in one of two ways: by using a comma followed by a conjunction or by using a semicolon.