Which of the following factors weaken(s) the hypothesis of ...

[penguins]

Which of the following factors weaken(s) the hypothesis of abiotic synthesis of organic monomers in early Earth's atmosphere?
1.    the relatively short time between intense meteor bombardment and the appearance of the first life-forms
2.    the lack of experimental evidence that organic monomers can form by abiotic synthesis
3.    uncertainty about which gases comprised early Earth's atmosphere
A) 1 only
B) 2 only
C) 1 and 2
D) 1 and 3
E) 2 and 3

[Millan]

I know it's D, we did this last week

[penguins]

Thank you, thank you!!