Which is a reason that protists are difficult to classify?

A: They are too small.
B: They are all eukaryotes.
C: They have been classified based on what they are not.
D: They have too many shared characteristics.

An adult inhales about 6.0×10−4 m3 of fresh air during a breath. only 20% of fresh air is oxygen. assume the pressure in the lungs is 1.0×105 paand the air is at a temperature of 300 k. how many oxygen molecules are in each breath? a. 1.4x10^23 b. 2.9x10^21 c. 4.9x10^-4 d. 2.9 x10^25