单项选择题
A.sing B.to sing C.sings D.sang
James Watt（）the steam engine. A.was inventing B....
单项选择题James Watt（）the steam engine.
A.was inventing B.invented C.had invented D.has invented
It is（）to interrupt the others while they are talking.A...
单项选择题It is（）to interrupt the others while they are talking.
A.rough B.rude C.polite D.troublesome
It was well known that Thomas Edison（）the electric lamp...
单项选择题It was well known that Thomas Edison（）the electric lamp.
A.invented B.discovered C.found D.developed
