The quantization process (a) converts the sample-and-hold output to binary code (b) converts a sample impulse to a level (c) converts a sequence of binary codes to a reconstructed analog signal (d)...

The quantization process
(a) converts the sample-and-hold output to binary code
(b) converts a sample impulse to a level
(c) converts a sequence of binary codes to a reconstructed analog signal
(d) filters out unwanted frequencies before sampling takes place