An experimental design was run to identify important factors affecting a particular response Y. The following design was run and tbe responses were recorded. Identify the design that was run.

A B C D Y

- - - - 46

+ - - + 95

- + - + 43

+ + - - 76

- - + + 73

+ - + - 56

- + + - 85

+ + + + 98

a) 2^k factorial design

b) placket burman design

c) central composite design

d) fractional factorial design