Your customer has implemented a solution that uses Cloud Spanner and notices some read latency-related performance issues on one table. This table is accessed only by their users using a primary key. The table schema is shown below. 

You want to resolve the issue. What should you do? 

Answer options:

A. Remove the profile_picture field from the table.
B. Add a secondary index on the person_id column.
C. Change the primary key to not have monotonically increasing values.
D. Create a secondary index using the following Data Definition Language (DDL):

D