When is it mandatory to operate the various speed retarders installed in the vehicle?

1. AWhen driving on a section of road before which a sign is posted warning of a sharp curve.
2. BWhen driving on a section of road before which a sign is posted warning of a winding curve.
3. CWhen driving on a section of road before which a sign is posted warning of dangerous skidding.
4. DWhen driving on a section of road before which a sign is posted warning of a steep descent.

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