In this task you will be given an answer to a question. You need to generate a question. The answer given should be a correct answer for the generated question.

Q: Red blood cells (RBCs), also called erythrocytes, are the most common type of blood cell and the vertebrate's principal means of delivering oxygen (O) to the body tissues -- via blood flow through the circulatory system. RBCs take up oxygen in the lungs, or gills of fish, and release it into tissues while squeezing through the body's capillaries.

A: where do you find red blood cells in the body
****
Q: The Waltons is an American television series created by Earl Hamner, Jr., based on his book Spencer's Mountain and a 1963 film of the same name, about a family in rural Virginia during the Great Depression and World War II.

A: what time period was the waltons set in
****
Q: San Pedro River is a northward-flowing stream originating about 10 miles (16 km) south of the international border south of Sierra Vista, Arizona, in Cananea Municipality, Sonora, Mexico. The river starts at the confluence of other streams (Las Nutrias and El Sauz) just east of Sauceda, Cananea. Within Arizona, the river flows 140 miles (230 km) north through Cochise County, Pima County, Graham County, and Pinal County to its confluence with the Gila River, at Winkelman, Arizona. It is the last major, free-flowing undammed river in the American Southwest, it is of major ecological importance as it hosts two-thirds of the avian diversity in the United States, including 100 species of breeding birds and 300 species of migrating birds.

A:
where does the san pedro river start and end
****