The repeating group of a crystal is called the
a. nucleus.
b. unit cell.
c. net.
d. crystal system.

The repeating group of a crystal is called the "crystal system". It should be noted that there can be many different types of crystal patters within the system. The main thing that binds them all together is symmetry. 

Advection fog occurs when warm air blows over a cold surface like snow and since tropical water is warm advection fog rarely forms over it

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