If computers ______, many problems on space flight could not have been solved. A: had not been invented B: are not invented C: were not invented D: have not invented

57. James watt ____ the steam engine. A: was inventing B: invented C: had invented D: has invented

When was the first bicycle invented The first bicycle was invented .

An American_______the bicycle. A: is invented B: invented C: invents

---Football______by the British at the beginning of last century. ---That’s probably why football is one of________popular games in England. A: was invented, the most B: invented, more C: was invented, more D: invented, the most

Where did the concept of feedback come from? A: It was invented by Confucius B: It was invented by Aristotle C: It was invented in World War 2 while working on anti aircraft guns D: It was invented to catch fish E: It was invented very recently in Alibaba’s research centre

Where did the concept of feedback come from？（ ） A: It was invented by Confucius. B: It was invented by Aristotle. C: It was invented in World War 2 while working on anti aircraft guns. D: It was invented to catch fish. E: It was invented very recently in Alibaba's research centre.

It is common knowledge that black tea in China more than 600 years ago. A: is invented B: was invented C: invents D: invented

It's common knowledge that black tea ______ in China more than 600 years ago. A: is invented B: was invented C: invents D: invented

____ was invented in 1917.