What does the frequency of a wave represent?
the distance between two consecutive crests
the number of wave cycles that pass through a specific point within a given time period
the distance between the highest and lowest points of a wave the length of wave that pass through a specific point within a given time period

Frequency of the wave represents the number of crests/troughs (waves) crossing a particular point in the medium in one second
This is actually the definition

A.(nh4)(2co3)is the correct answer 

Answerd. may include all of these are many definitions of bases: the  brønsted-lowry definition of acids and bases says that bases are proton acceptors.the arrhenius definition of acids and bases says that bases increase [oh⁻] in solution (thereby producing oh⁻ ions)the lewis definition of acids and bases says that bases donate electron pairs.therefore, the sensible answer is that a base may include all of the described characteristics.