What is the standard acceptable age range for testing concrete cylinders designated as '28-day' compressive strength specimens?
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A
Cylinders must be broken on exactly day 28 — no tolerance allowed
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B
Cylinders may be tested between 26 and 30 days and still qualify as the 28-day break
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C
Cylinders should be tested between 27 and 35 days for statistical accuracy
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D
Cylinders must be tested at exactly 30 days to ensure full curing