If We Assume the Traditional View of Existential Import, Why

Multiple Choice

If we assume the traditional view of existential import, why is the following syllogism invalid? All radioactive isotopes are dangerous to humans.
No radioactive isotope is a common gas in the atmosphere.
No common gas in the atmosphere is dangerous to humans.

A) undistributed middle
B) illicit major term
C) illicit minor term
D) two negative premises
E) negative premise with affirmative conclusion, or negative conclusion with no negative premise