The given statement is interrogative, it asks a question ('won't we' is a contraction of 'will we not'; 'will' can be used to create a question in the future tense). Hence the statement will end with a question mark '?' and no change is required. So, option D is correct.
Option A contains a full stop '.'; full stops are used in declarative and imperative sentences.
Option B contains an exclamation mark '!'; this punctuation mark is used in exclamatory sentences.
Option C: 'plane' ends with an ellipsis mark '...' which is used to indicate an omission of words in a line or paragraph. The ellipsis mark is used in the end of a sentence to indicate a trailing off of thought. The sentence that has an ellipsis at the end will still require a full stop, exclamation mark or question mark to end the sentence:
'... .' - for statements,
, '...!' - for exclamatory sentences and
'...?' - for questions
If you replace the word 'plane?' by 'plane...', it will be incorrect because the question mark must still be there to indicate the end of the question.
Hence options A, B and C are incorrect.