I would say B because c and d would decrease competition and a would do the same, or just kill the ecosystem.
Hope this helps and don't forget to hit that heart :)
This is true i think if that is a question
A - 1 CH4+ 1 O2 = 1 CO2+2 H2
b - 2 Al+3 Cl2 = 2 AlCl3
c - 1 CH2O+ 1 H2 = 1 CH3OH
*The ones that have the coefficient of 1 you can leave blank but if you have to put a number just put 1
No because you are supposed to do this

T for time and V for velocity or acceleration so what you do is take the two numbers
D= 3/12 it goes 12 meters every 3 seconds so you devide 12/3

So for every second the ball roles 4 meters!
Hope this helps! :)