The classification of air mass types is based on which parameter?
a) amount of snow or rainfall
b) source region
c) temperature extremes they cause
d) distance traveled
e) moisture content

20 ( B )

Explanation:

Given data:

a and b are 10 map units apart

b and c are 20 map units apart

a and c = 30 map units apart

condition ; Triple heterozygote testcrossed

number of progeny = 1000

Determine the number of double crossover result

P( crossover between a and b ) = 10/100 = 0.1

P( crossover between b and c ) = 20/100 = 0.2

p( double crossover ) = 0.1 * 0.2 = 0.02

hence number of double crossovers = number of progeny * 0.02

                                                              = 1000 * 0.02 = 20