Which of the following is true?

water is important to some organisms.
some substances must be dissolved in water before they can be used.
all organisms obtain water through food.
plant cells are unaffected when water is scarce.

The most appropriate answer would be "Some substances must be dissolved in water before they can be used".  

Water is one of the most essential substances for all organisms. It helps in performing all the major functions of the living system such as digestion, excretion, transportation et cetera.

Water is considered as a universal solvent as it can dissolve a maximum number of substances as compared to any other solvent.

It is the reason that it is used as a solvent to dissolve substances which can not be used in their raw form.

For example, NaCl is administered in hospitals in the form of saline.

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.