Which of these is an example of human phenomena that can be described in spatial terms a population b trade flows c cities and towns d all of the above

The correct answer is - D. all of the above.

In essence, spatial terms in geography refers to the describing of things that are relating to areas.

So population, trade flows, cities and towns, can all be observed as things in an area. Population can be seen area by area, so that the density, ethnicity, education etc can be seen and compared between areas. The trade flows usually are divided into trade zones, or trade areas, and cities and towns all belong to a certain area.

separation of church and state? not sure what you mean.