Is it acceptable to modify "bonus" with "positive"

Before I jump to my question, a short note about cloze tests from Wikipedia:

A cloze test (also cloze deletion test) is an exercise, test, or assessment consisting of a portion of text with certain words removed (cloze text), where the participant is asked to replace the missing words.

Question: I was looking at my friend's English test paper that was prepared by some Chinese teachers. The text for the cloze section was adopted from an article published in Chicken Soup for the Soul: Raising Great Kids: 101 Stories about Sharing. The article can be accessed via Google Books. On that page, the author modifies "bonus" with "positive". The usage doesn't seem right to me.

The Chinese teachers treated that portion this way:

So, when someone does reciprocate, it is an enormous and positive ______.

A. effect B. bonus C. attitude D. contribution

Of course, the suggested answer was in accordance with the original text, which is B. What do you think?

Thanks!

The context of the linked text is that when reciprocation isn't expected, it is very much appreciated when it does occur, so it seems the author intended positive to convey the idea of emotionally uplifting. It's a bonus because it wasn't a calculated part of the exchange. Unfortunately, positive bonus ends up being redundant as @deadrat observes, so is a poor choice for a 'cloze test'.

Here's an example of a "cloze test" (link). Importantly for the OP, the original text isn't shown. If the construction of the original text is poor, the test question looks weird.

Nevertheless, let's look at the choices in your question:

So, when someone does reciprocate, it is an enormous and positive ______.
A. effect B. bonus C. attitude D. contribution

(A) would be valid if the sentence read "it has an ...";
(B) would be fine without the words "and positive";
(C) "enormous ... attitude" doesn't sit well here — it has the idea of arrogance; and
(D) is plausible, though whether "it is an enormous ... contribution" depends on how much the reciprocating person contributes.

Of these, I'd say option D is least bad.

In the example, positive is correct and is not used as the converse of negative but is used in the sense of

OED

2. Explicitly laid down; expressed without qualification; admitting no question; stated, express, definite, precise; emphatic;"

1867 E. A. Freeman Hist. Norman Conquest I. App. 637 A strong presumption, though it is by no means positive proof.

2021 Greybeard EL&U "I am positive that he he is guilty."

and British Dental Journal The length of the gingivally approaching clasp arm can therefore be increased to give greater flexibility which can be a positive advantage when it is necessary to clasp a premolar tooth

Generally speaking, Chinese English tests' cloze texts are full passages. The student wouldn't be encountering this sentence in isolation. If it were, Lawrence is right that A, B, & D would all be acceptable words; A would be less good because is suits it less well; B would be less good because there's no base level mentioned for the bonus to be added to; and D could be (awkwardly) assumed to refer to whatever effort or relationship is being reciprocated.

However, within context,

The best thing is that you feel so great about doing something for someone else [that] you don't even look for or expect anything in return[, s]o when someone does reciprocate it is an enormous and positive _______________.

bonus (B) is the best answer, however awkward or redundant that positive may strike you. The preceding sentence is focused on a base reward (feeling good) and the reciprocation is a second good thing in addition to it, an unexpected bonus. In contrast, effect (A) would require the initial sentence to focus on leading up to the reciprocation and contribution (D) would require at least mentioning the thing being built up.