Correct answer:
B) eight
Details:
The source you are examining is a primary source, direct testimony from an industrial worker named Matthew Crabtree during hearings held in Britain by the Sadler Commission. The reliability of the commission testimony comes from the first-hand experience of the witness, Mr. Crabtree.
The Sadler Commission testimony by Matthew Crabtree took place on May 18, 1832. Matthew Crabtree was 22 years old at the time, and is recalling factory work he did beginning at age 8 (as he stated in his testimony). His experience was very visceral and vivid, so it's likely these memories were etched firmly into his mind.
The purpose of the Sadler Commission and the witnesses called forward (such as Mr. Crabtree) was to get at the facts of what factory life was like. It was meant to inform the government of the truth about factory conditions and child labor.
The statements made are taken as reliable fact. Mr. Crabtree was testifying before a government commission, so adherence to the truth was expected, and facts were asked for.
The experiences of child labor in a factory could have provoked very emotional testimony, but Mr. Crabtree presented the facts of his working life in factory labor in a neutral way, giving matter-of-fact answers to questions he was asked.
The evidence Mr. Crabtree provided were detailed, personal examples from his own experience.