The Exploratory Life-Sciences Experiments Aboard the Viking Spacecraft Landers Found

The exploratory life-sciences experiments aboard the Viking spacecraft landers found evidence of

A) a very sterile environment in which life could not have existed and a very chemically inert soil, reacting with almost no reagents.
B) primitive life-forms such as elementary bacteria that should not be a hazard when humans explore Mars.
C) very reactive chemistry in the Martian surface rocks, but no evidence of life or remnants of life-forms.
D) primitive life-forms that had existed on Mars earlier in its history but had not survived.