But ________ we spend a third of our lives sleeping, it seems that...

• A. however
• B. although
• C. yet
• D. while

Answer: (B)

This tests using a concessive connector to show contrast between a fact and what follows. Although fits because it introduces a clause that acknowledges a real fact—spending a third of life sleeping—while still highlighting a surprising or contrasting point in the main clause that comes next: it seems that … The presence of but signals contrast, and although provides the natural link to the opposing idea in the dependent clause.

The other options don’t fit as smoothly here: however is a sentence-level connector and sounds awkward inside the same clause; yet is possible but less formal and natural in this position; while can express contrast but doesn’t convey the same concessive nuance as although.