Options (A) and (B) use a negative construction “no question of it not being possible,” which is wordy and awkward because it creates a double negative. This reduces clarity.
Option (D) is similar to (C) but “whenever you want” is more natural and flexible than “when you want,” which sounds slightly restrictive.
Option (C) is concise, positive in tone, and direct: it clearly expresses certainty (“Undoubtedly”) followed by the statement of possibility without extra negatives or redundant words.
This makes (C) the clearest and most concise version.