Sometimes we fill a second multiple choice dropdown with the options corresponding to the choice the user made in the first dropdown. This technique allows you to choose the first option in the second dropdown automatically.
In the Bind Expressions of the first dropdown field, On Change/Click box, enter the jquery that selects the first entry in the second dropdown. The format is,
Get the ID of the second dropdown by right-clicking on the field in Chrome, and choosing, "Inspect" from the pop-up menu.
If this is not working for you, it might be that you need to delay this line of code a bit to give the dropdown time to requery its contents first. Try this technique to slow it down a second. Adjust the time as necessary.
// Something you want delayed.
}, 5000); // How long do you want the delay to be (in milliseconds)?