HELP PLS THANK YOUU :))) THANKS

So i have a lot of answers answered but it says i still need to answer more questions. why is it doing that? how many questions need to be answered?

What is the most common blood type in the u.s.?

Melanocytes and keratinocytes work together in protecting the skin from uv damage when keratinocytes a. provide the melanocyte with a protective shield against abrasion b. maintain the appropriate temperature so the product of the melanocyte will not denature c. maintain the appropriate ph in order for the melanocyte to synthesize melanin granules d. accumulate the melanin granules on their superficial portion, forming a uv-blocking pigment layer