you should speed up your work ,or you will not finish it on time .
he slowed down his car .
he kept speeding up his car ,which was dangerous
the plane flew higher and higher / lower and lower .
he raised / lowered hight of the flight .
007gdh2020-03-06👍786 1. Speed up/slow down 2. You should speed upthe progress of your work,otherwise we won’t be able tofinish on time. 3. Heput the speeddown. 4. He continued toimprove the speed,it is very dangerous 5. The planeis flying high/flyinglow. 6. Heincreased/decreasedflight altitude