If the same sequence of rock layers is observed over a large area,
a.
they are probably not related
b.
a large deposit of rock formed over a large area
c.
conditions of formation were probably very different
d.
it is just a coincidence

b.  a large deposit of rock formed over a large area

Explanation:

If the same sequence of rock layers is observed over a large area, a large deposit of rock formed over a large area.

b.  a large deposit of rock formed over a large area

Explanation:

    Sedimentary rocks are, by comparison with the other types, the least resistant and those that suffered the most from wear processes. In addition, they cover about ¾ of the earth's surface, although in volume they exist in smaller quantities than metamorphic and magmatic rocks.

   Sedimentary rocks have as one of their main features their layered structure, ie, it is a type of stratified rock (see figure below). These layers are the result of the slow and gradual interposition, which takes thousands and thousands of years, of the different sediment layers. These interpositions are often responsible for “burying” or covering the bodies of animals and plants, giving rise to fossils. Studying sedimentary rocks is thus one of the most effective ways to study the historical, geological and biological past of the planet.

littering streams           is the answer