The correct option is
A Signature / name
Here, we have to explain the format of the letter. The 24th blank in the letter is the place where we usually write the date. Let's have a look at the options.Option B - Date should always be written after the address in an informal letter. In the end, the last blank must be filled with the sender's name/signature. Hence, option B is incorrect.
Option C - 'Sender's address' is written on the top left side of the paper. Hence, option C is incorrect.
Option D - 'Receiver's address' is not needed in an informal letter as we usually write informal letters to our friends and family members. Hence, option D is incorrect.
Option A - In the last blank, the sender must do his signature or write his name. Hence, option A is correct.