"Fluid intelligence involves being able to think and reason abstractly and solve problems. This ability is considered independent of learning, experience, and education. Examples of the use of fluid intelligence include solving puzzles and coming up with problem-solving strategies."
- Verywell Mind
Average speed is defined as total distance moved in total interval of time
so it is given as

now here is we show distance by "d" and time by"t"
then we will have mathematical expression as follows

I think its between b or c