Question about I-485

I filed I-140 in August(still pending) and now I want to file 485. In I-485, which box should I check under part 2, application type, a or h? your advice would be greatly appreciated. My case is employment-based.

a. an immigrant petition giving me an immediately available visa number has been approved(Attach a copy of the approval notice.....)

h other basis of eligibility. Explain