Which of the following can ensily reverse motion and are better at varying speeds than electrical motors?

Which of these is most responsible for differences between the twentieth century to the twenty-first century?

Peter is thinking of a number which isless than 50. the number has 9 factors. when he adds 4 to the number, itbecomes a multiple of 5. what is thenumber he is thinking of ?

Why is a multiview sketch drawinf different from other sketches like isometric, two point, and oblique