Medela breast pump?

Megan • Wed, Dec 09 • Pregnant with babies #2&3 after a long (8 years) road with IVF and 4 miscarriages. Ready to enjoy these 9 months!

The breast pump I had with my son had the option to pump one or both sides. Does the medela pump allow you to choose, or do you have to use it as a double pump?