Correct Answer: heard

Solution : The correct choice is the third option .

The sentence indicates that the person received a letter, and now, finally, they "heard back" from the person mentioned in the letter. Heard back in this context means that the person has received a response or communication from the mentioned individual.

The meanings of the other words are as follows:

• Herd: This refers to a group of animals, particularly cattle, sheep, or other similar animals, that live, move, or are kept together.
• Hard : This refers to something that is firm, solid, not easily yielding to pressure or bending, or difficult to break or cut.
• Horde : This refers to a large group, crowd, or multitude of people, often used in the context of a disorderly or unruly mass of individuals.

Therefore, the complete sentence would be: "Today I received a letter. Finally, I heard back from him."