Which of the following is a characteristic of a mixture?
a) can have varying properties
b)has a fixed composition
c) contains no pure substances
d) both a and b

a) can have varying properties

Explanation:

Mixture:

A mixture is substance made up of two or more kind of substances. In mixture the substances are physically combine with each other and can not react chemically. That's why every substance retain their properties in mixture and thus properties of mixtures can vary according to the addition of substances.

All other options are incorrect because,

b)has a fixed composition

Mixture can not have fixed proportion. The amount of substances that form mixture can be vary.

c) contains no pure substances

Mixture consist of pure substances because all substituents are combine physically and when separated they remain same as they were.

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).