Question

complete the text with the better conjunctive adverb. most people are aware of the eight basic blood types: a, ab, b, and o, each of which can be
egative\ or \positive.\ ______, each of these eight types can actually be classified into millions of varieties based on the antigens that coat red blood cells. however after all

Explanation:

"However" is used to introduce a statement that contrasts with what has been said before. Here, the first - part mentions the eight basic blood types, and the second part presents a contrasting fact that these types can be further classified into millions of varieties. "After all" is used to introduce a statement that supports or explains a previous statement, which is not the case here.

Answer:

However