The correct option is
A Sender's name/Signature
The format of a postcard has been attached.
Option A: The second blank must be filled with either the sender's name or his signature, as required in the format of a postcard. The signature named 'Jimmy' can be seen in the format. Hence option A is correct.
Option B: The sender's address is not mentioned on a postcard. Hence option B is incorrect.
Option C: The message (most important information) is written between the date (1) and the sender's name (2). It isn't written in blank 2. Hence C is incorrect.
Option D is incorrect because the answer lies in A.