The correct options are
B Top, left-hand
D Top, right-hand
A formal letter can be written in two ways: The Indented or Traditional style and the Block style.
Options B and D:
In the traditional style, the sender's address is written on the top, right-hand side of the letter.
(The closing salutation and the sender's sign or name is written on the bottom right-hand side.)
In the Block style, the sender's address is written on the top, left hand side.
(The closing salutation and sender's sign and name are written on the bottom left-hand side.)
Hence, both options B and D are correct.
Options A and C: On the 'bottom, left-hand hand', the signature or name of the sender is written.
The same is written on the 'bottom, right-hand side' of a block style letter.
Hence options A and C are incorrect.