Answer:
4
Step-by-step explanation:
1 is true. Speed is the magnitude of velocity so if the magnitude of velocity(speed) changes, then velocity changes itself.
2 is true.
![a _(avg) = (v _(f) - v _(i) )/(t)](https://img.qammunity.org/2023/formulas/physics/college/qbu0hf4sqz6tr5jun340uxt1gyjayli6bh.png)
Since speed changes, the inital and final speeds are different, therefore we will have some nonzero acceleration because the numerator does not equal zero.
3 is correct, acceleration is a vector so it has direction, meaning if the direction of speed changes then we will have acceleration.
4. is false, a constant velocity has a acceleration of 0.
5 is correct, motion along a straight line is linear.