1) It is linear because the voltage increases by 0.41 volts every 2.5 minutes.

2) It is linear because the voltage decreases by 0.8 volts every 0.4 minutes.

3) It is exponential because the voltage decreases by 20% every 2.5 minutes.

4) It is exponential because the voltage increases by 20% every 0.4 minutes.

Solution: Choice C is correct.

We know that, standard form of an exponential equation is y = a . bx.

Therefore, the given function, v = 0.41 . 0.8(2t/5) is exponential and not linear.

Also, since b=0.8 < 1, the function will be a decreasing function (means voltage will decrease as time increases)

Now when 2t/5 increases by 1, the voltage is multiplied by .8 or 80%).

Therefore, the voltage decreases by 20% in that interval.

Now, to find out the interval, 2t/5 = 1

Or t = 2.5 minutes.

Therefore, the given function is exponential, with the voltage decreasing by 20% every 2.5 minutes.