The correct option is B 3, 4
The set of 4 digit number is from 1000 to 9999.
From 1001 to 9999, the predecessor of any 4 digit number is a 4 digit number only.
But for 1000, the predecessorr is 999 which is a 3 digit number.
So, the predecessor of a 4 digit number can be a 3 digit or a 4 digit number.