When preparing for a climb, many climbers will measure the air pressure at the highest altitudes to which they will be climbing. why do they do this?

Because even at high altitudes there is still plenty of oxygen for breathing. However, pressure is what drives the oxygen into the blood stream. At lower pressure we aren't able to breath because the pressure is not high enough to get the O2 into the blood.

Explanation:

c

explanation:

i believe the answer is c and this is only worth 10 points you might wanna change it

.) the observation by semmelweis that more mothers died of childbed fever when their doctors also worked in the morgue