Single-row functions operate on single rows and return one result per row. Let's look at each option in the context of Oracle 12c SQL:
A . CONCAT: This function can only combine two values at a time. If you need to concatenate more than two values, you have to nest CONCAT functions or use the || operator.
B . MOD: The MOD function returns the remainder of a division operation, not the quotient.
C . CEIL: This function returns the smallest integer that is greater than or equal to a specified number. It works with both positive and negative numbers.
D . FLOOR: It returns the largest integer that is less than or equal to the specified number, not greater than or equal to.
E . TRUNC: This function can indeed be used with both NUMBER and DATE values to truncate them to a specified number of decimal places or to a particular component of a date.
Reference:
Oracle Database SQL Language Reference 12c Release 1 (12.1), Functions
Oracle Database SQL Language Reference 12c Release 1 (12.1), CONCAT Function Oracle Database SQL Language Reference 12c Release 1 (12.1), MOD Function Oracle Database SQL Language Reference 12c Release 1 (12.1), CEIL and FLOOR Functions Oracle Database SQL Language Reference 12c Release 1 (12.1), TRUNC Function