When is it obligatory to operate the vehicle’s different types of decelerators or retarders ?

1. A When driving on a road section before which a “sharp curve” sign is placed.
2. B When driving on a road section before which a “danger of slipping” sign is placed.
3. C When driving on a road section before which a “hairpin curve” sign is placed.
4. D When driving on a road section before which a “dangerous descent” sign is placed.