Answer:
The correct answer is D) let.
The phrase "Nature will never let her forgive herself" implies that Nature will not allow or permit her to forgive herself. In this context, "let" means to allow or give permission.
The other options, "admit," "allow," and "tolerate," do not convey the same meaning as "let" in this sentence. "Admit" means to confess or acknowledge, "allow" means to give permission or grant access, and "tolerate" means to accept or endure. None of these options fit the intended meaning of the sentence, which is about Nature not allowing her to forgive herself.