The correct option is
A Go straight, turn left and you will reach the park.
There are three moods in English:A verb which makes a statement of fact or asks a question or expresses a supposition which is assumed as a fact, is in the indicative mood.
A verb which expresses an instruction, a command, a request or a prayer, is in the imperative mood.
A verb which expresses a wish/hope/ desire/ resolution is in the Subjective mood. They include verbs like wish, hope, suggest, ask, demand, recommend, insist, advise, propose, etc and are mostly followed by the word, "that". It also states a condition/wish which is contrary to the fact. Example: "I wish that I were a millionaire".
Option A: The verbs, "go straight" and "turn left" gives instructions to the listener to follow and reach the park. Hence, this is in the imperative mood. Option A is correct.
Option B: The phrase, "By going straight and turning left", assumes as a fact that you do so and then states the results (you will reach the park). This sentence assumes a fact and states the consequence of the same. Hence, it is in the indicative mood. Option B is incorrect.
Option C communicates a question of whether one can go straight, turn left and thereby reach the park. Hence, this is in indicative mood (more specifically also referred to as interrogative mood).
Option D is in subjunctive mood as there is a hope expressed i.e "I hope that by going straight and turning left I can reach the park". Hence this is not the correct answer.