Identify how many choices are given at each step in a dichotomous key. a.1
b.2
c.3
d.4

Dichotomous keys consist of a series of statements with two choices in each step that will lead users to the correct identification.

so your answer would be: option 2

b. 2

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me

i need with 1.3.2 investigate cycling o2 and co2 apex

we need to see it