The Golden Gate Bridge, the first sight for many people arriving in the United States by ship, is a well-recognized landmark, which spans(横跨) the Golden Gate Strait.
The idea for a bridge across the strait had been around for many years, but it was not easy to get the project started. The construction of the bridge finally began in 1933. The construction work set new standards for safety----workers were among the first required to wear hard hats, and an innovative（革新的） safety net saved the lives of nineteen men while the bridge was built. The Golden Gate Bridge was completed in 1937, which was finished ahead of schedule.
Joseph Strauss was the chief engineer in charge of the bridge project. However, he had little experience with the construction of suspension（悬浮）bridges. For this reason, other engineers, architects, and designers made great contributions to the design and construction of the bridge. For example, the bridge owes its art style and unique orange color to the architects Irving and Gertrude Morrow. Charles Alton Ellis was the main engineer on the project and did much of the technical work necessary to build the bridge.
Today, the Golden Gate Bridge has a main span of 4,200 feet and a total length of 8,981 feet, making it one of the longest bridges in the world. The bridge is 90 feet wide, and its span is 220 feet above the water. The towers supporting the huge cables (巨缆) rise 746 feet above the waters of the Golden Gate Strait, making them 191 feet taller than the Washington Monument. About 40 million cars cross the bridge every year. There are foghorns（雾角）to let passing ships know where the bridge is, and aircraft beacons（信号灯）on the tops of the towers to stop planes from crashing into them.
The purpose of the passage is to _______.

A．describe the construction work of the Golden Gate Bridge

B．introduce the Golden Gate Bridge

C．tell us the history of the Golden Gate Bridge

D．introduce the engineers in charge of the Golden Gate Bridge

Safety innovations during the construction of the bridge included ________.

A．hardhats and a safety net	B．aircraft beacons
C．foghorns	D．all of the above

It can be inferred from the passage that _______.

A．Joseph Strauss was skilled in the construction of suspension bridges

B．it took the construction workers three years to build the Golden Gate Bridge

C．about 100 thousand cars cross the Golden Gate Bridge every day

D．the Golden Gate Bridge is the longest bridge in the world

The underlined word “them” in Paragraph 4 refers to ________.

A．towers

B．cables

C．waters

D．bridges