IMO B because COMMA+AND needs two independent clauses.

What is the source of the question?

I doubt this construction ..

A bruk can remember when it cached a particular piece of food in a particular place, researchers have discovered,and tend not to bother to recover a perishable treat if strongly long enough to have rotted

IMO A

Main subject A buck... main verbs remember and tend... shud be parallel..

Let some more answer come in but I can hint answer is the ones that you have suggested.

PAB2706 wrote:IMO A

Main subject A buck... main verbs remember and tend... shud be parallel..

Considering the parallelism you said above, the sentence should split as under,

A bruk can remember .. and A bruk can tend .. .

The part in red is wordy .. it should be like this,

A bruk can remember .. and tends ..

This sentence is captured in B.

A bruk can remember when it cached a particular piece of food in a particular place, researchers have discovered,and they tend not to bother recovering a perishable treat strongly long enough to have rotted.

The two statements in different colours are independent clauses. However, I am doubtful of what the pronoun they refers to. Ideally it should refer to plural form of bruk. I don't know what a bruk is but I perceive it some singular entity.

Please correct incase I am wrong.

IMO A

@Bublii suggested COMMA + AND usage but its not actually COMMA + AND thing happening here. If u notice the part "researchers have discovered"....this part is quoted in COMMA's so if u chop off this part then u chop off the COMMA's also. Though i also believe the question is poorly structured.

IMO A

+1 for A,

theyin B is wrong