Examples of how humans negatively affect local ecosystems are A. Building dams, deforestation cutting down trees), adding point sources to nearby streams to allow for run-off, building roads and structures, and salting roads
B. Planting trees and other plants to attract native species
C. Creating laws to prohibit fishing from local streams
D. Removing non-native species from the environment.​

A.  Building dams, deforestation cutting down trees), adding point sources to nearby streams to allow for run-off, building roads and structures, and salting roads.

Explanation:

Removing non-native species from the environment helps the native ants to thrive without having any changes in the ecosystem effect them (i.e. new invasive animal).

Creating laws to prohibit fishing from local streams helps keep the fish alive and allowing them to continue to use this stream.

Planting trees and other plants to attract native species helps secure and grow the ecosystem of that area.

This leaves A as the answer.

Hope that helps you!

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom

c) 50% there are four chromosomes. after crossing over, 2 of the four have been changed. that means any gamete has a 2 in 4 chance or 50% chance of receiving the mutated chromosome.