What is the function of the trombone slide?

The trombone is a wind instrument, whose sound is generated through the impulse of air by the person who uses it through its mouthpiece. In itself, this instrument has a low sound, which is regulated by its slide: the longer the slide is lengthened, the more air will enter the instrument tube, making the sound more low-pitched. On the contrary, the less the slide movement is lengthened, the higher the sound will be. Thus, the slide fulfills the function of regulating the tones of the sound emitted by the instrument.

i think a and b is the answer