I want to enter one of two values in column A and one of two
(different) values in column B.

In column C I want Excel to compute a value for each of the 4 possible
combinations of values in columns A and B on a particular row.

Eg

if A1 = urgent and B1 = important, C1 = 'Q1'
if A1 = non-urgent and B1 = important, C2 = 'Q2'