Consider the following figure of a stirred-tank bioreactor and identify $A, B, C$,and $D$.

• A
  $A \rightarrow$ Motor,$B \rightarrow$ Culture broth,$C \rightarrow$ Impeller,$D \rightarrow$ Foam breaker
• B
  $A \rightarrow$ Foam breaker,$B \rightarrow$ Motor,$C \rightarrow$ Culture broth,$D \rightarrow$ Impeller
• C
  $A \rightarrow$ Motor,$B \rightarrow$ Foam breaker,$C \rightarrow$ Impeller,$D \rightarrow$ Culture broth
• D
  $A \rightarrow$ Motor,$B \rightarrow$ Foam breaker,$C \rightarrow$ Culture broth,$D \rightarrow$ Impeller