Antonyms

Derivative means something that is derived or copied from another source, lacking originality. Original is the direct opposite, referring to something that is the first of its kind or not copied. Imitative (A) is actually similar to derivative, while spin-off (E) and by-product (E) are types of derivative things.

Conserve means 'not allowing to deplete'. So, it is the correct opposite.

Desultory means lacking a plan, purpose, or regular pattern - random and haphazard. Methodical (B) is the opposite, meaning systematic, orderly, and following a logical plan. Chaotic (C), indiscriminate (A), and random (D) are all similar to desultory, while halfhearted (E) is unrelated.

Desuetude means a state of disuse, discontinuance, or lack of use. 'State of being active' (A) is directly opposite - being in use and functioning. Disuse (B) actually means the same as desuetude, while contemplate (C) and 'a state of mind' (D) are unrelated.

Dilate means to expand, widen, or become larger. Contract (A) is the opposite - to shrink, narrow, or reduce in size. Open (D) is similar to dilate, while remove (B) and delight (C) are unrelated to the concept of expansion.

Option 3 is the correct answer as all others are synonyms.

Deprave means make someone immoral.... So, opposite is moralise/honest.

Disconcert means to unsettle, disturb, or make someone feel uncomfortable or confused. Please (A) means to give satisfaction or pleasure - the opposite emotional effect. Offend (B), grieve (C), and remove (E) are negative actions similar to disconcert, while concert (D) is just a word look-alike.

Disconsolate means very unhappy, depressed, or sorrowful. Content (A) is the opposite - happy, satisfied, and at peace. Unhappy (B), miserable (C), melancholy (D), and disturbed (E) are all synonyms or similar negative emotions, not opposites.

Discountenance means to disapprove of, discourage, or show disapproval toward someone or something. 'Favour somebody' (A) is the opposite - to support, approve, or show approval. Embarrass (B) is negative, while 'disapprove of somebody' (C) is actually the meaning of discountenance, not the opposite.

Dilatory means slow,拖延, or given to wasting time - delaying action. Prompt (C) is the opposite - quick, punctual, and ready to act without delay. Tardy (A), remiss (B), laggard (D), and lazy (E) are all similar to dilatory - all mean slow or delaying.

Opaque is the opposite of diaphonous. Rest all are synonyms of diaphonous. 

Disheveled means untidy, messy, or in disordered appearance (especially hair or clothes). Neat (A) is the opposite - tidy, organized, and well-groomed. Tousled (B), messy (C), unkempt (D), and uncombed (E) are all similar to disheveled, meaning the opposite of neat.

Dissemble means to conceal, disguise, or pretend - to hide one's true thoughts or intentions. Reveal (C) is the opposite - to show, expose, or make known. 'Hide something by pretense' (A) is actually the definition of dissemble, not the opposite. Evade (B), quibble (D), and dither (E) are all forms of concealment or avoidance.

Deride means to make fun of, so  opposite is admire/approve.