The CHOOSE function uses the first argument in the function to select an
appropriate value from the other arguments in the list.
Zero represents the first valid argument in the list.
CHOOSE(0,"Buy","Sell","Hold") would return "Buy" since zero
corresponds to the first value in the list.
CHOOSE(A1,10,20,30) would return '10' if the value of cell A1 was
zero, '20' if the value was 1, and '30' if the value was 2.
CHOOSE(A1,B2:F2) would return the value of ERR regardless of
the value of cell A1, since the function does not accept range
references.