Which of the following is a vector quantity?
speed
distance
acceleration

C) Acceleration
For example, if person A is the observer, then he/she can predict the distance or speed or time by simply looking at it. But at the same time, the observer can't predict the acceleration of a moving object as he/she can't determine the direction of the object. So, without a direction, the acceleration can't be predicted. For example, displacement, force, velocity, momentum, etc. are vector quantities.
◙ But, Distance, speed and time are only specified with their magnitude. For example, work, volume, density, mass, etc. don't need a direction for their representation.
So, (c)Acceleration is the answer.

Neptune is the eighth planet from the sun. it was the first planet to get its existence predicted by  mathematical calculations  before it was actually seen through a telescope on sept. 23, 1846. irregularities in the orbit of  uranus  led french astronomer alexis bouvard to suggest that the gravitational pull from another celestial body might be responsible. german astronomer johann galle then relied on subsequent calculations to   spot neptune via telescope. previously, astronomer galileo galilei sketched the planet, but he mistook it for a star due to its slow motion. in accordance with all the other planets seen in the sky, this new world was given a name from greek and roman mythology — neptune, the roman god of the sea.