Question: People without safe drinking water may get an illness called dysentery. Dysentery is caused by a type of amoeba that lives inside the body. Doctors can find these amoebas by looking at body samples under a microscope. Which characteristic of amoebas best explains why doctors use microscopes to find dysentery amoebas?

  Options: 
 A. Amoebas can change their shape.
 B. Amoebas need humans to survive.
 C. Amoebas look just like human cells.
 D. Amoebas are made of only one cell. 
Answer: D