20.4 21.3 are the correct answers
The period during which the presence of stromatolites decline is the Proterzoic period. Stromatolites are widely distributed sedimentary structures consisting of laminated carbonate or silicate rocks, produced over geologic time by the trapping, binding, or the precipitating of sediment by groups of microorganisms, primarily cyanobacteria.
The Use of nitrogen fertilizers near the lake is your answer.
Hello!
If you look at a zipper, you'll see that it doesn't have a wheel or an axle. A zipper links the <span>protruding teeth that the zip contains. Your answer would be B!
You can feel free to let me know if you have any questions regarding this!
Thanks!
- TetraFish</span>
