I'll try to explain, because I've had tubes before. In fact, I still have them.
For me, tubes were put in because of too many ear infections, and excessive water in my ear. The tube helped drain the water out. You can see A picture I have in a file. The tubes can be put I believe in the ear drum. They're put there to help drain water that has trouble getting out on its own.
Answer:
The beaver population increased
The amino acid sequence in protein from the gene fragment for botana curus
is the same with species Z that is valine, histidine, leucine, threonine, proline,
glutamine and glutamine. Meanwhile, species X and species Y has different amino
acid sequence compared to botana curus. Therefore, species Z is most closely
related to botana curus because both species has the same amino acid sequence
and has similar sized DNA fragments.