Respuesta :
Hi!
The statements that are correct are 1, 2, and 5.
Statement 1 is correct, is once the crabs arrived; the change in the environment (which wasn't there before as the mussels hadn't evolved to have thicker shells already, if the crabs were in the environment beforehand they would've already adapted), caused some mussels to grow thicker shells, a new trait, changing the distribution of traits.
Statement 2 is correct as well. In this case, the mussels underwent natural selection; where those with traits better suited to the environment survived and others didn't. That is how more of the mussel population grew shells; they aren't able to just change their traits if they want to, it's survival of the fittest.
Statement 5 is the final correct statement. The mussels adapted to their environment, and developed a thicker shell to help protect against the crabs, and you can tell it did help them survive because over time more mussels ended up with that trait; if it didn't help them survive then all those with that trait would've died off and there wouldn't be any remaining.
Hope this helped!