Answer the following question given this paragraph: 

Flagella ( flagellum , singular) are long, thin structures that protrude from the cell membrane. Both eukaryotic and prokaryotic cells can have flagella. Flagella help single-celled organisms move or swim towards food. The flagella of eukaryotic cells are normally used for movement too, such as in the movement of sperm cells, which have only a single flagellum. The flagella of either group are very different from each other. Prokaryotic flagella, shown in Figure below , are spiral-shaped and stiff. They spin around in a fixed base much like a screw does, which moves the cell in a tumbling fashion. Eukaryotic flagella are made of microtubules that bend and flex like a whip.


Q: What are the long, thin structures that protrude from the cell membrane and help single-celled organisms move or swim towards food?

 Choices:

- microvilli

- tentacles

- sporangia

- flagella

A:
flagella
