Read the following passage about Self-driving cars and mark the letter A, B, C or D on your answer sheet to indicate the option that best fits each of the numbered blanks from 18 to 22.

Self-driving cars, once seen only in science fiction, are now being developed and tested on roads worldwide. A key player in this field, Waymo, launched its first autonomous taxi service in 2020, ___(1)___. These cars rely on a complex system of sensors, cameras, and artificial intelligence to navigate streets and avoid obstacles. Self-driving cars promise to revolutionize transportation by reducing accidents, saving time, and ___(2)___.
However, their widespread adoption is still hindered by technical challenges and regulatory hurdles. ___(3)___, companies like Waymo, Tesla, and Cruise are investing heavily in developing technology that can ensure the safety and reliability of these cars. ___(4)___, autonomous vehicles must be able to handle complex traffic scenarios, adapt to unpredictable road conditions, and interact safely with human drivers and pedestrians. ___(5)___.