An index fossil is: a. a fossil found in a particular site. b. a fossil used to categorize a stratigraphic layer. c. the ideal specimen of that species that all examples must follow. d. the type specimen of a species.

An index fossil is important and useful for dating and correlating the strata of which it belongs.

The index fossil have a narrow time range and a wide spatial distribution. An index fossil is used in the identification of related geologic formations.

Hence, (c) an index fossil is an ideal specimen of that species that all examples must follow.

b is dominant over the allele for the white fur.

answer: ice crystals in air

the water from the water body or another source of water gets evaporated as water vapor as an effect of heat on water. these water vapor rises in the upper layers of the earth atmosphere under high atmospheric pressure. the atmospheric pressure of these water molecules starts to decrease due to the effect of cold air. the invisible water vapor condenses into visible water droplets and ice crystals.these ice crystals and water droplets being less denser than the surrounding air floats on air as clouds.