Select the correct option:

The committee issued several directives, none of _______ were implemented.

Correct Option: which

Explanation:

To choose the correct relative pronoun for this sentence, let us analyze the sentence structure and grammar rules regarding quantifiers with pronouns:

1. The sentence contains two clauses joined together: "The committee issued several directives" and "none of _______ were implemented."

2. The blank follows the phrase "none of", which refers back to the non-human noun "directives".

3. In English grammar, when a preposed quantifier phrase (like "none of", "all of", "many of", "some of") introduces a dependent relative clause referring to things or non-human objects, we use the relative pronoun "which".

4. Why other options are incorrect:
- "them": Using "them" creates a comma splice or run-on sentence without a coordinating conjunction (e.g., "and none of them were implemented"). Since there is no conjunction connecting the clauses, a relative pronoun is required.
- "whom": "Whom" is used to refer only to people, whereas "directives" refers to non-living items/rules.
- "that": The pronoun "that" cannot be used directly after a preposition like "of" in non-restrictive relative clauses (we do not say "none of that").

Therefore, "which" is the grammatically correct word to complete the sentence: "The committee issued several directives, none of which were implemented."