50. Which of the sentences is appropriate for Sentence 7 as the concluding sentence of the paragraph?(A) Till now, many companies are still finding the best way to upgrade the manufacturing procedures by Alexa.(B) That is the reason why Alexa is crucial for drivers to multitask and to be available on the road.(C) With the invention of Alexa, a safer way is paved for drivers in navigation and vehicle control.(D) In the long run, Alexa will be successfully installed to high-end cars for free to ensure the driving quality.