3. Gases pass in and out of a leaf through the
a) stomata
o c) xylem
b) phloem
d) cuticle

a) stomata

Explanation:

The stomata are little pores / doorways / openings that have the express purpose of allowing gases in and out. Without this, plants would not be able to fix carbon, which is essential in respiration.

Why not c or b: The xylem and phloem channel water through the plant, not gases.

Why not d: The cuticle is the waxy outer layer of the leaf meant to protect it, not allow gases through.

relative dating involves things like higher layers are most recent than rocks lower in the sequence. this can be extended to the known sequence of fossils. rocks containing rabbit fossils are later than those containing dinosaur fossils.  

absolute dating methods mainly use radioactive elements that have known rates of decay and produce recognizable products. for example potassium 40 decays to produce argon. once a rock has solidified the argon is trapped. by measuring the argon and potassium0 you can get an accurate number for the age.  

some other methods are good for archaeological ages. dendrochronology involves recognizing the sequence of tree rings. the orientation of magnetized particles in baked clay can be used to date a fire.

hope this .. .