15(D2-D1) 20(D2-D1) 5(D2-D1) 10(D2-D1)
Answer Discuss in Comment
special maintenance recurrent maintenance period maintenance routine maintenance
20 10 40 30
upper face middle face lower case all of the above
1000kg 7850kg 8850kg 2000kg
light soft heavy hard
urban area semi-urban area rural area all of the above
rubble ashlar random square rubble
4 3 2 6
block glass ground glass coloured glass flint glass
"Scientists dream about doing great things. Engineers do them."