A microbiologist tested 4 substances to find out if they would kill certain types of bacteria. The substances were applied to a plate on which bacteria would normally grow. One week later, the scientist recorded the results in the diagram below.

Based on the diagram, which conclusion is most likely to be correct?
A.
Substance D was able to kill all 3 types of bacteria.
B.
Substance A was able to kill two of the three bacteria types.
C.
Substance B was unable to kill any bacteria.