1. Respiratory dust particles that can reach alveoli have the sizes of
a) less than 2 nanometers
b) less than 2 microns
c) less than 5 microns
d) less than mm
2. Which of the following hormones can enter the targetcell?
a) thyroxine
b) estrogen
c) both a and b
d) neither a nor b
Please give a brief explanation!