What is the frequency of an event?
a. probability
b. degree
c. expected occurrence
d. identification

Option A, Probability

Explanation:

Probability defines the possibility of occurrence of an event.  

Let "n" be the total number of desired outcome of an activity and "A" is the sum of all possible outcomes. Thus, in this case probability is defined by following mathematical relation –  

For example -  

Calculate the probability of occurrence of head when a coin is tossed one timed ?

Here, Total number of desired outcome i.e head when a coin is tossed once  

1 digestive system

2 stomach

3 bladder

4 carbon deoxide

5 tiger

if your own plato the answer is b. the fern transitioned from sporophyte generation to gametophyte generation.