4. The environmental problems created late in the twentieth century are
a. impossible to solve.
b. partly a result of increased
human population.
c. not as bad as those created early in
the twentieth century.
d. both a and b above

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the dna molecules have a negative charge because of the phosphate groups in their sugar-phosphate backbone, so they start moving through the matrix of the gel towards the positive pole. power is turned on and dna fragments migrate through gel (towards the positive electrode).

explanation:

what? are the statements?

all these collisions do one thing, and that thing is explained in the last option. when dusst, rocks and ice collide, they harden and form giant layers of rocks or hard ice.

d)   to harden materials to form different parts of earth’s layers

hope it ,

bioteacher101