Which option expiration date should I use?

The Trade Alert says that I should choose April expiration dates, and on my broker’s trading platform I see several April expiration dates. Which date does the Trade Alert mean?

Unless the Trade Alert explicitly tells you to use a weekly expiration date, then you should use the monthly options. Monthly options expire on the third Friday of the month. In this case, you would choose the expiration date that’s the third Friday of April.

You can also see the exact date in the Trade Alert’s option symbol: the middle characters in DIA170421P191 mean 2017-04-21.