The correct answer is (a) Four
To explain: In earthwork calculations, the unit of lift is 2 metres for the first lift and one extra lift for every 1 metre. Therefore, when the earth is to be lifted for 4.5 metres, four lifts are to be paid to the contractor. For the first 2 metres, one lift is needed and for the rest 2.5 metres, three more lifts are required which sums up to a total four lifts.