Question

What is the subject in this sentence: Along the way, stop and take in the breathtaking views.

Answer 1

Some sentences have a subject that is not written but understood. This is one of those sentences. The subject of this sentence is " you ".

Along the way, YOU stop and take in the breathtaking views.

some sentences that give an order or a request are set up like this.
Go to bed....subject is " you "
Please take out the trash....subject is " you "

Answer 2

if the answer chouces are:
 A. stop
B. views
C. an understood you
D. way

The answer is C. An understood you. It is called like this, because the word "you" does not actually appear in the sentence, but it's there nonetheless, it's "understood" that it's there. In this sentence, the subject is "you" and the verb is "stop and take". 

Hope this helps.