In a sense, scientists and engineers in the past have been fortunate, for we became accustomed to being measured by nature itself-- an unwaveringly fair and consistent, （） unforgiving, judge.

A. expiration
B. explanation
C. expertise
D. expenditure

A. Both interferon and conventional treatments should be used to ensure the survival of the patients.
B. At the end of three years, only ten to thirty percent of the patients who had not received interferon died.
C. Only the patients who received interferon survived.
D. Most of the patients who were treated with interferon survived.