Question

complete the text with the best 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.
after all as a result however

Explanation:

The first sentence states the common knowledge of 8 basic blood types, while the second introduces a lesser-known, more detailed classification (millions of varieties). This shows a contrast between common awareness and a surprising additional fact. "However" is the conjunctive adverb used to signal such a contrast. "After all" is used to emphasize or explain a prior point, and "As a result" indicates a cause-effect relationship, neither of which fits the context.

Answer:

However