recommended but not required by law.
10
A flashing yellow light means you should drive with caution when approaching and moving through the intersection.
Electric field, a directional vector
At a level crossing, the same rules apply to trucks as do to cars, in that the Train always has the right of way. As long as there's no indication of a train coming, (lights flashing, etc) the truck does not have to stop. However, some trucks, particularly those carrying dangerous goods, are required to stop regardless of whether or not the lights are flashing, to check to make sure there is in fact no train coming. If this is the case, there will be a sign on the back of the truck warning that it stops at all railroad crossings.
Recommended, yes. Required, no.
The use of starting fluid should not be required, and is not recommended.The use of starting fluid should not be required, and is not recommended.
Not alwaysButLoud noises are always an indication the repair is required
A flashing light at night attracts attention to oncoming cars and motorists to alert them that there is a biker present. It is required because especially at night it may be hard to see bikers and the flashing light will definitely help avoid possible accidents.
prerequisite is required
The board is at rest to create movement significant force (hitting the board) is required to propel it in directional motion.
ObviousAnother answer:'Obvious' is an adjective, while 'clear indication' is a noun phrase, so the previous answer is not a synonym; a noun is required. 'Evidence' is a possible answer, though not applicable in every context.
At least 13 but its recommended not required