What is the right course of action here?

In this situation, the key rule is priority at an intersection with signs or indications.

You must allow both the yellow car and the blue truck to pass first because:

- The blue truck is on the main road or has a priority sign, so it has the right of way.
- The yellow car, coming from the right, also has priority over you according to the general right-before-left rule at an uncontrolled intersection or the priority sign that applies.

Your intention to turn left means you must yield to oncoming traffic going straight or turning right.

The option to “proceed before the yellow car” is incorrect because the yellow car has priority as it comes from the right side.

Remember: When turning left, always wait for oncoming vehicles and vehicles from the right if they have priority markers or no signs indicating you have priority.

Your answer is correct because you identified the need to allow both the yellow car and blue truck to proceed first, following German right-of-way rules.