Every time I turn on macbook pro I get menu for choosing startup disk
Going out on a limb here due to lack of information, just trying to help.

Your Mac is 4 Years old, and probably (if you are like me) you have a "lunch" stuck under the right Option key.

Clean it.

https://www.ifixit.com/Guide/How+To+Fix+Sticky+Keyboard+Keys+on+a+MacBook/37709

If that did not help you might have to replace the key.