Arrange the sentences A,B,C and D to form a logical sequence between sentences $1$ and $6$.
- The main source of power in industrial undertaking is electricity.
- Electricity from water also requires enormous river valley projects involving huge expenditure.
- In contrast, electricity from atomic power stations will result in a tremendous saving in expenditure.
- Besides, the mineral resources of the world required for generation of electricity are being rapidly depleted.
- But the production of electricity needs huge quantities of coal.
- The installation of atomic plants will help in meeting the shortage of these resources.