In the given sentence, the correct pronoun to fill in the blank is "that."
Explanation:
1. The sentence reads, "We hope to come back to _______ special picnic spot someday."
2. The pronoun is referring to the noun "special picnic spot."
3. When we refer back to a singular noun like "special picnic spot," we use the singular pronoun "that."
4. So, the sentence should be: "We hope to come back to that special picnic spot someday."
Therefore, the correct answer is B. that.
