The 74138 is a 3-to-8 decoder. Together, two of these ICs can be used to form one 4-to-16 decoder. To do this, connect

a. one decoder to the LSBs of the input; the other decoder to the MSBs of the input

b. all chip select lines to ground

c. all chip select lines to their active levels

d. one chip select line on each decoder to the input MSB