According to IS 456 : 2000, for a nominal 1.5-hour fire resistance, the nominal covers specified for the simply supported beams, slabs and ribs are _______.
1
20 mm, 25 mm and 40 mm
2
20 mm, 25 mm and 35 mm
3
20 mm, 25 mm and 20 mm
4
20 mm, 20 mm and 40 mm