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 however as a result

Explanation:

• "After all" is used to emphasize a reason or explanation. Here, there is no such context of giving a reason.
• "However" is used to show a contrast. The first part says people know about eight basic blood - types (a simple classification), and the second part says they can be classified into millions (a more complex classification), which is a contrast.
• "As a result" is used to show a consequence. There is no cause - effect relationship here in the sense of one thing leading to the other in a result - oriented way.

Answer:

However