Does your title mean "doubt" or drought"? Use a dictionary.
Your sentence has little meaning without context and it should start with a capital letter.
Student or Learner
today is one of the memorable days.
IS THIS SENTENCE IS CORRECT? OR TELL ME THE CORRECT ANSWER?
And there is no reason at all for your final two sentences to be in capital letters. Writing in all capitals is considered to be the online equivalent of shouting.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
How about Today is a memorable day?