Researchers tested four kinds of concrete formulations for compressive strength (MPa) at 7 days and 90 days of curing: Mix I, 18 (7d), 32 (90d); II, 22, 50; III, 26, 35; IV, 17, 48. The team argued that for engineering structures requiring long-term strength, 7-day strength is a poor predictor of 90-day strength, and engineers should select on 90-day data. The strongest support is ______
Which choice most logically completes the text using the data above?
- A
Mix II's 90-day strength of 50.
- Bcheck_circle
the rank reversal: Mix III had the highest 7-day strength (26) but mid-pack 90-day strength (35); Mix IV had the lowest 7-day strength (17) but the second-highest 90-day strength (48)—7-day rank does not predict 90-day rank.
- C
Mix III's 7-day strength of 26.
- D
the average across mixes.
Explanation
"7-day strength is a poor predictor of 90-day strength" requires showing rank reversal. Choice B captures this directly: III leads at 7 days but lags at 90 days, IV is the opposite.