Mark the letter A, B, C, or D on your answer sheet to indicate the cor

Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.    

"In the year 1900, the world was in the midst of a machine revolution. (11) _____ electrical power became more ubiquitous, tasks once done by hand were now completed quickly and efficiently by machine. Sewing machines replaced needle and thread. Tractors replaced hoes. Typewriters replaced pens. Automobiles replaced horse-drawn carriages. 

A hundred years later, in the year 2000, machines were again pushing the boundaries of (12) _____ was possible. Humans could now work in space, thanks to the International Space Station. We were finding out the composition of life thanks to the DNA sequencer. Computers and the world wide web changed the way we learn, read, communicate, or start political revolutions. 

So what will be the game-changing machines in the year 2100? How will they (13) _____ our lives better, cleaner, safer, more efficient, and (14) _____ exciting? 

We asked over three dozen experts, scientists, engineers, futurists, and organizations in five different disciplines, including climate change, military, infrastructure, transportation, and space exploration, about how the machines of 2100 will change humanity. The (15) _____ we got back were thought-provoking, hopeful and, at times, apocalyptic. "

• A. A. what
• B. B. that
• C. C. who
• D. D. which

Mệnh đề danh từ => bắt đầu với "what"
=> A