Fill in the blanks with suitable words.

The car was running ___________40 km/h.

Correct option is C

The correct preposition to use in this context is "at". When referring to speed or a rate of movement, we typically use the preposition "at." The phrase "running at 40 km/h" means that the car was traveling at that specific speed.

Explanation:

• "at" is the correct choice when specifying speed or a measurement of velocity. We commonly say "at 40 km/h" or "at 60 miles per hour."
• The prepositions "on" and "up" are not typically used when discussing speed. For instance, "on" is used to indicate a surface (e.g., "on the road"), and "up" often refers to direction (e.g., "up the hill").
• "at" directly communicates the rate or speed at which something is happening.