How did the PDP-8/S computer process its 12-bit data?

A. In parallel, using a 1-bit Arithmetic Logic Unit (ALU)
B. In parallel, using a 12-bit Arithmetic Logic Unit (ALU)
C. Serially, using a 12-bit Arithmetic Logic Unit (ALU)
D. Serially, using a 2-bit Arithmetic Logic Unit (ALU)
Answer: 