The most cost$-$effective approach to reducing the project duration by $1$ day is:

Crash activity A $1$ day at a total cost of $$4,500$

Crash activities A and $D1$ day each at a total cost of $$2,300$

Crash activity B $1$ day at a total cost of $$750$

Crash activities C and D $1$ day each at a total cost of $$1,300$

Crash activities D and E $1$ day each at a total cost of $$800$