Which of the following is a heterogeneous mixture? a) vinegar and water b) milk c) oil and vinegar d) air

The correct option is C, OIL AND VINEGAR
There are two types of mixture, homogeneous and heterogeneous mixtures.
Homogeneous mixture are uniform in composition and an example of this is milk.
Heterogeneous mixture refers to a mixture which is not uniform in composition, that is, smaller constituent parts is present in it and it can be easily separated using suitable methods.

The most plausible answer is b, duration. the given amount of time is considered how long it last for.

Ibelieve the answer is d