7. which one of these units is not expressed in metric system? a) km b) in c) nm d) mm

The correct option is: B) in        

Explanation:

The metric system, also called the International System of Units, is an international system of measurement.

The units for length measurement used in the International System of Units are: kilometre (km), metre (m), centimetre (cm), millimetre (mm), nanometre (nm).

Whereas, the Imperial units and U.S. customary units of length include inch (in), which is equal to 25.4 mm.

answer; specialization of production;

b.

developed countries have tended to improve the environment, while developing countries have tended to damage it.