Answer:
towards
Explanation:
A preposition can be defined as a word that shows or illustrates the relationship between a pronoun or noun and other words in a sentence.
The main purpose of a preposition as a part of speech is to introduce an object (of, upon), indicate a timeframe (from, by, over), show direction (to, across, along), location or place (at, up, after, below) and to illustrate the spatial or sequential relationship between two or more things, people, place, etc.
Some examples of a preposition used in various literary works in English language are up, below, after, by, against, for, over, at, to, towards, etc.
Hence, the most appropriate word to fill the blank is "towards" and the complete sentence would be written as; "The ball is running towards us."
In English language, towards is a preposition that is used to describe the direction in which something or someone moves.
