A yellow left-curve sign with a 25 mph advisory plaque indicates:

Correct answer: D – A left curve with an advisory speed of 25 mph
The yellow warning sign shows that the road curves left. The plaque below it gives a suggested safe speed of 25 mph for the curve; it does not establish a minimum speed. Reduce speed further when snow, ice, rain, or other conditions make the roadway less safe.
Source: Montana Driver Manual — Ch. 3, “Warning Signs”, Montana Driver Manual — Ch. 5, “Controlling Speed”



