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: 50% of all trees are very resistant, 30% of trees are somewhat resistant, and 20% are susceptible to invasion by pest. The probability that a tree will be at least somewhat resistant is:

A) P = 0.3.
B) P = 0.5.
C) P = 0.8.
D) P = 0.7.