A Geneticist Is Conducting Research on Pest-Resistant Walnut Trees

Multiple Choice

A geneticist is conducting research on pest-resistant walnut trees. He has developed a set of trees, when crossed, to produce offspring as follows: 40% of all trees are very resistant, 30% of trees are somewhat resistant, and 20% are susceptible to invasion by pest, for the rest, susceptibility status is undetermined. The probability of a tree from a crossing being not resistant or an unknown status is:

A) P = 0.2.
B) P = 0.3.
C) P = 0.4.
D) P = 0.5.