Some scientists_________________us that the thermal blanket around the globe_____________________. the average temperature of the earth to rise.
were warning / has caused
had warned / caused
have warned / may cause
have been warning / was causing
If transport costs_____________ into consideration at the outset, the plant____________. far from its present site.
will be taken / are being built.
had been taken / would have been built
have been taken / have been built
were being taken / will be built
The first laser ______________. in 1960 by Maiman, almost half a century after the publication in 1916 of Einstein`s theory of radiation which ________________. the possibility of laser operation.
has been demonstrated / had shown
had been demonstrated / showed
was demonstrated / showed
demonstrates / was shown