You Go Hiking with Some Friends in a Nearby National

You go hiking with some friends in a nearby national park. The weather is cool when you set out but it quickly becomes very warm. Neither you nor your friends are carrying enough water. Eventually you find a stream and because you are so thirsty, you drink from it. About a week later you start to feel unwell. You have vomiting, abdominal cramps, and explosive diarrhea (loud, severe diarrhea) . Your stool seems kind of oily and is difficult to flush away. You tell your RN brother about your signs and symptoms, and he tells you he thinks you may have giardiasis, caused by the protozoan Giardia lamblia.
-You ask your brother which method of eliminating microbes is the best in general. He tells you that there is no one perfect method and that various factors must be taken into account when considering any antimicrobial approach. These include all of the following EXCEPT 

A) the type of microbes to be controlled.
B) environmental conditions such as temperature.
C) whether a potential infection can be easily treated.
D) situational considerations (is a method practical for the situation?) .
E) the number of microbes to be controlled.