The oxygen crisis occurred around A) 2 billion years ago B) ...

[awywial]

The oxygen crisis occurred around
 
  A) 2 billion years ago
  B) 3.5 billion years ago
  C) 2.5 billion years ago
  D) 4 billion years ago

Question 2

In most extrasolar planetary systems the center of mass is likely to be located
 
  A) midway between the star and its most massive planet
  B) close to the center of the parent star
  C) exactly at the center of the parent star
  D) close to the center of the most massive planet

[ttt030911]

Answer to Question 1

A

Answer to Question 2

B

[awywial]

TYSM

[ASDFGJLO]

Thanks for the timely response, appreciate it