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A number of scientists found genes in the 18th and 19th centuries. Scientific discoveries were made one after another in the 18th and 19th centuries. Many scientists succeeded in finding out how the features of living things were passed on to the next generation in the 18th and 19th centuries. It took a long time for scientists to find out why members of the same family look like each other.
must be may have been can have been could be
was warned; would not take had been warned; would not have taken would be warned; had not taken would have been warned; had not taken
Birds hardly pay attention to their young. Baby crocodiles can look after themselves well. Some dinosaurs took care of their young. Birds and crocodiles take good care of their youn
warned are warned have warned have been warned
was warned; would not take had been warned; would not have taken would be warned; had not taken would have been warned; had not taken
was warned; would not take had been warned; would not have taken would be warned; had not taken would have been warned; had not taken
was warned, would not take had been ,warned, would not have taken would be warned, had not taken would have been warned, had not taken
was warned; would not eaten had been warned; would not have eaten would be warned; had not eaten would have been warned; had not eaten
was warned; would not take had been warned; would not have taken would be warned; had not taken would have been warned; had not taken
Birds hardly pay attention to their young. Baby crocodiles can look after themselves well. Some dinosaurs took care of their young. Birds and crocodiles take good care of their youn
was warned; would not take had been warned; would not have taken would be warned; had not taken would have been warned; had not taken
there have been decreased returns in the research of fundamental science there are too many important things for scientists to study applied science and engineering take up too much time and energy today’s scientists are not as intelligent as those in the past
most of the best things have already been changed most of the best things remain to be changed there have never been so many best things waiting to be discovered most secrets of the world have already been discovered
have been known to scientists for many years have only recently been discovered are known by us will probably remain a mystery
to award to be awarded to have been awarded to have awarded
was warned; would not take had been warned; would not have taken would be warned; had not taken would have been warned; had not taken
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