In the presence of a base, blue litmus paper will.

O turn purple

stay blue

to turn red

In the presence of a base the blue litmus paper would remain blue.

Explanation:

This is because the litmus paper will react depending on the pH of the solution added. If the solution is acidic pH 7 the litmus paper will turn blue. If the litmus paper is blue when a base is added it will remain blue.

In the presence of a base, blue litmus paper will turn red ...