What does this traffic sign combination indicate?

Your answer is correct. The triangular sign warns of a railway crossing ahead, and the round sign with "10" indicates a speed limit of 10 km/h. According to German traffic rules, this means you may approach the railway crossing at a maximum speed of 10 km/h (option 1) and also cross it at a maximum speed of 10 km/h (option 2). The speed limit applies to both approaching and crossing the railway tracks to ensure safety. Option 3 is not correct because the signs restrict the speed of road traffic, not the rail traffic. Remember, always reduce your speed when approaching railway crossings and adhere to the indicated speed limits for safe passage.