This is, in my opinion, a rather controversial topic.
Although in this case I prefer the first one, I think both can work, depending on how you view the common noun "keywords."
If "keywords" is considered the main noun (i.e. the head) in that noun phrase (NP), then "A" and "B" seem to modify the noun "keywords" and the use of the article is justified: the keywords identified as A and B.
However, I think it is also possible to conceive of that NP as a unit, in which case the article can be eliminated, as is the case when you say, for example:
- Is Room 1 close to Room 2? (notice the use of the capitals, which in the absence of an article are advisable)
On this page (a Canadian style manual), which is mainly about the use of capitals, we can find some related phrases which show that the article is omitted when the NP is taken as a unit:
- Back to Square One.
- He’s on Cloud Nine.
This also reminds me of a somewhat related thread I once took part in which you might find of interest.