Which transaction isolation level should you use in sp1?

You use SQL Azure to store data used by an e-commerce application.
You develop a stored procedure named sp1. Sp1 is used to read and change the price of all the products sold
on the e-commerce site.
You need to ensure that other transactions are blocked from updating product data while sp1 is executing.
Which transaction isolation level should you use in sp1?

A.
Repeatable read

B.
Read committed