If the pressure is not ________ immediately, there may be an explosion.

A) understand B) understanding C) understood D) to understand

A) managed B) attained C) succeeded D) achieved

A) writing B) write C) to write D) to have written

A) harm B) damage C) danger D) injury

A) has interrupted B) had interrupted

C) would have interrupted D) should have interrupted

A) in vain B) in advance C) in case D) in effect

A) should have left B) need have left C) would have left D) must have left

A) failing B) failed C) did fail D) had failed

A) from B)for C) at D) on

A) is it B) is there C) it is D) there is