Here are the changes as directed:
Who can forget Mahatma Gandhi? (assertive) Everyone remembers Mahatma Gandhi.
I wish I were young again. (exclamatory) Oh, how I wish I were young again!
Why waste time in this futile operation? (assertive) There is no point in wasting time in this futile operation.
How wet and cold you are! (assertive) You are very wet and cold.
It was possible. (negative) It was not impossible.
Was he not rude to say this? (assertive) He was rude to say this.
There was no one present who did not applaud. (affirmative) Everyone present applauded.
He is too weak to move about. (negative) He is not strong enough to move about.
Is this the kind of behaviour expected of you? (assertive) This is not the kind of behaviour expected of you.
Everybody will admit that this is a good idea. (negative) Not everybody will deny that this is a good idea.
I long for a good book to read. (exclamatory) How I long for a good book to read!
This can never happen. (interrogative) Can this ever happen?
How can I put up with this? (assertive) I cannot put up with this.
Well done, Ray! (assertive) Ray has done well.
I am yearning for a short holiday. (exclamatory) Oh, how I am yearning for a short holiday!
Shall I ever forgive him? (assertive) I wonder if I will ever forgive him.
None will deny that he is a dignified person. (affirmative) Everyone will agree that he is a dignified person.
As soon as he arrived, he began to argue. (negative) No sooner had he arrived than he began to argue.
We are not here to waste time. (interrogative) Are we here to waste time?
You will never forget this wonderful boat ride. (interrogative) Will you ever forget this wonderful boat ride?
These changes involve transforming the sentences by considering their meanings and phrasing them appropriately as per the instructions. Assertive sentences state facts or beliefs, exclamatory sentences express strong feelings, and interrogative sentences ask questions, whereas negative transformations often involve adding 'not' in a meaningful way.