Câu hỏi: Choose the letter A, B, C or D the word that has the underlined part different from others.

My grandmother enjoys __________. She waters the plants when she has free time.

Robots through the Middle Ages were used primarily for entertainment. However, the 20th century featured a boom in the development of industrial robots. Industry has benefited drastically from the expanse of a robotic work force. Automated machines have taken over dangerous and boring jobs from humans. Because robots never get tired, extra shifts have been added to factories. Farmers have taken advantage of new technology with automated harvesters. The medical industry benefits from advancements in assisted surgical robotics. The military has launched various programs in robotic technology.

Why have factories added extra shifts?