Here's a problem to solve: 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?

Among the 4 following options, which is the correct answer?

- 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.
 