You find a sedimentary rock that contains pieces of igneous rock. what is the best explanation for how pieces of igneous rock got there?

There are dozens

Explosive materials such as pumices, lapilli and ashes may be blown by volcanoes thousands of kilometers around and fall in a sedimentary basin.
Erratic are all sorts or rocks transported by glaciers and abandoned wherever the lower altitude will stop their front. Rivers also transport materials from one basin to another. So does the wind.
Rocks of continental origin, such as sandstones, conglomerates etc. are all sedimentary rocks and may well contain igneous fragments.

c. genetic engineering

explanation:

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.