Scientists infer that oxygen in earth’s atmosphere
did not exist in large quantities until after
(1) the first multicellular, soft-bodied marine
organisms appeared on earth
(2) the initial opening of the atlantic ocean
(3) the first sexually reproducing organisms
appeared on earth
(4) photosynthetic cyanobacteria evolved in
earth’s oceans

Photosynthesis is the process of converting carbon dioxide into oxygen. Oxygen didn't really exist in the atmosphere until photosynthetic organisms appeared and evolved.

Humid continental climate is found in the interior of continents between the 30 and 60 degrees latitude, but usually above the 40 degree line.   40 degrees north of the equator means less direct sunlight and therefore less warmth.   this climate is mainly found in the northern hemisphere since there are no major landmasses in the southern hemisphere.  if you live in northern indiana, you know all about humid continental because that is the climate type you have!

Iwould say d. eye contact and body language because you aren’t using any spoken communication. hope this : )