填空题

Automatic Doors in Egypt
When you next step through the doors of a supermarket,spare a thought for Heron,a talented specialist of ancient "high tech" engineering. Nearly two thousand years ago he designed automatically opening doors for the temples of the Egyptian city of Alexandna.
Heron had a talent for designing mechanical wonders to surprise people and make people happy. (46) was a gift to the Egyptian priests,who for centuries had used wonder mechanical or otherwise,as a way of strengthening their authority.
Employing relatively simple mechanical principles, Heron devised a means (47) as if by unseen hands--when the priest lit a fire on the altar outside the temple. The fire heated the air in a metal globe placed beneath the altar ,foreign the water in it through a pipe into an enormous bucket. The bucket was suspended by chains from a system of weights and pulleys, which turned the doors on their pivots as the bucket became heavier.
A second surprise took place when the altar fire was put out. (48) , the water was sucked the other way through the pipe. When the bucket emptied,it went upward,making the pulley system move in reverse,and the doors closed again.
Another design included in Heron’s writings could make a trumpet blow when the temple doors opened--a combination of musical doorbell and burglar alarm.
There need be little doubt that the automatic-door system described by Heron was actually used in Egyptian temples and (49) Heron himself referred in passing to a similar system used by other engineers.. "Some instead of water use quicksilver (mercury)"Using mercury (50) would certainly have made it more efficient.
A．whereby the doors of a small temple would open
B．possibly elsewhere in the Greco--Roman(希腊—罗马的)world
C．His design for automatic temple doors
D．because of the quick heating of the air inside the globe
E instead of water in a machine similar to Heron’s design
F As a result of the sudden cooling of the air in the globe