The correct options are
A Once you complete your homework, you can go down to play.
B Complete you homework before you go down to play.
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 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 sentence gives an instruction about what is allowed ('you can go down to play') once the homework is completed. Hence, it is in imperative mood. Hence, option A is correct.
Option B: The phrase, "Complete your homework" advises the listener what to do before going down to play. Hence, this is in imperative mood. Option B is correct.
Both options A and B are correct.
Option C" The phrase, "I wish" is in subjunctive mood as there is a wish expressed. Hence this is not the correct answer.
Option D is incorrect as options A and B is the correct answer.