Which is a drawback to the use of oil shale to produce energy? oil shale can be mined only in arid regions. processing, mining, and waste disposal are expensive. most of the world’s oil shale occurs in politically unstable countries. oil shale occurs only in areas with plentiful water resources for processing.

The answer is; Oil shale occurs only in areas with plentiful water resources for processing.

The refinement of oil shale requires a lot of water. This is used to quench the products of retorting and pyrolysis and also reduce dust. The water used becomes heavily polluted and has to be treated before discharge, otherwise, it will be the cause of a major environmental disaster to the local areas.

white blood cells or wbc s are mainly 2 types-

1.agranulocytes

2.granulocytes

the monocytes or macrophages of agranulocytes , dendritic cells which are accessory leucocytes, and b cells which is one type of lymphocytes   identify the antigens present on the pathogen's surface. these three cells are called antigen presenting cells(apc) which are phagocytes and destroy the antigens by secreting antitoxins. besides this leukocyte is always plays vital role in the immunity of the body.