what valid summary address (below) contains the longest prefix?

Click the Exhibit button. Given the four networks listed, what valid summary address (below) contains the longest prefix?

A.
10.1.0.0/20

B.
10.1.0.0/16

C.
10.1.1.0/23

D.
10.1.16.0/19

E.
These networks cannot be summarized.