Read the following statements and find out the correct ones:
$A.$ Spontaneous generation theory was approved once and for all.
$B.$ Pasteur showed that in pre-sterilized flasks,life did not come from killed yeast.
$C.$ Oparin observed the formation of amino acids by creating electric discharge in a closed flask.
$D.$ Life appeared $500$ million years before the formation of the earth.

• A
  $B$ and $D$ are correct
• B
  $A$ and $C$ are correct
• C
  Only $A$ is correct
• D
  Only $B$ is correct