When we see sedimentary rock units that are twisted or tilted, we know that some force must have disturbed the strata after they were deposited. the principle upon which we base this inference is the principle of

The principle of original horizontality says that most sedimentary layers of rock are collected in a horizontal position. Example of sedimentary rock is Limestone layers form in flat layers at the bottom of a shallow sea. Limestone had gray layers and this is revealed in the Mojave desert, pointing up at an angle from the desert floor. 

the answer is b. hope this !

81 is a composite number.