Correct!

You're riding a motorcycle that's towing a trailer. What should you do before turning right onto a dual carriageway?

Stop, and then select a very low gear
Position in the left gutter of the side road
Assess the width of the central reservation
Correct answer
Check that there's enough room for vehicles behind you

DVSA theory test explanation

Before emerging right onto a dual carriageway, make sure that the central reservation is wide enough to protect both your motorcycle and its trailer. If it's not, you should treat it as one road and check that it's clear in both directions before pulling out.