2. The concrete must thereafter be kept continually moist for ( A ). A. at least 14 days B. only 14 days C. about 14 days D. less than 14 days
3. To keep concrete moist, ( C ).
A. we can only spread some sand or burlap over the surface. B. we spray (喷)?some water over the surface. C. we should spray water on the surface frequently. D. we should spray water mixed with sand over the surface. 4. After the concrete is placed, ( B ) A. it should be covered for a long time.
B. it must be covered to avoid the strong sun light. C. it should be covered for 3 days.
D. it may be covered for the first 3 days if possible. 5. Special curing compounds ( B )
A. can only be used from the moment to concrete first begins to set. B. can be used even after the concrete has been placed in service. C. can always be used on the concrete highway. D. can be sprayed on anything.
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