According to the investigation, the D-train accident resulted from the fact that the authorities concerned didn’t _________ enough importance to the safety of the signal equipment.
.Without any doubt, depression________can create a variety of negative health effect.
________passenger plane crashed near Gazvin, Iran and all 168 people on________board were killed.
--How often do you drop your English teacher a line? ---________. But usually once a week.
Some English scientists are identifying problems ____ technology in the 21st century. If solved, the solutions could change the world.
Exactly ____they did when at last they reached the sea remains a complete mystery.