单选题 For a certain class of junk bonds, the probability of default in a given year is 0.2. Whether one bond defaults is independent of whether another bond defaults. For a portfolio of five of these junk bonds, what is the probability that zero or one bond of the five defaults in the year ahead?

A、

A. 0.5904.
B、

B. 0.7373.
C、

C. 0.0819.

【正确答案】 B

【答案解析】
The outcome follows a binomial distribution where n=5 and p=0.2. In this case p(0)=0.8⁵=0.3277 and p(1)=5×0.84×0.2=0.4096, so P(X=0 or X=1)=0.3277+0.4096.