如题49图所示多杆机构中，机构自由度的数目是（）。 A．0 B．1 C．2 D．3

关于合创伤，哪项是错误的

A．台创伤影响牙周炎症的扩展途径和组织破坏程度

B．合创伤可引起牙周炎症

C．慢性合创伤常因牙磨损、牙齿突出等因素所致

D．急性合创伤常因修复体等医源性因素所致

E．继发性合创伤是因牙周组织支持力不足所致

使“计算机技术”在当前窗体上输出的语句是（ ）。

A．MenuOne．Visible=Tree

B．MenuOne．Visible=False

C．MenuOne．Enabled=True

D．MenuOne．Enabled=False

阅读理解。

                                                    Foreign attacks on U.S.soil

       1812—During the War of 1812, British forces (军队) burned the new capital at Washington, D.C. They

also attacked Baltimore and New Orleans and captured (占领) Detroit, which at the time was a remote military

outpost (前哨基地). 

       1846—A brief invasion (入侵) by Mexican troops across the Rio Gande began the U.S. — Mexican War

in 1846. But the remaining action in that conflict (冲突) occurred in California, New Mexico and in Mexico.

California and New Mexico belonged to Mexico at the time. 

       1916—Mexican revolutionaries led by Pancho Villa attacked the town of Columbus, N.M., on March 9,

1916.

       1941—Japan attacked Pearl Harbor in Hawaii on Dec.7, 1941, killing nearly 2,400 people and forcing

America into World War II. 

       1993—Terrorists (恐怖主义者) blew up a truck bomb in the basement of the World Trade Center in

February 1993, killing six people and injuring more than 1,000. 

       2001—Terrorists hijacked (劫机) several planes on Sep.11, 2001. Two ploughed into (撞入) New

York's World Trade Center (WTC), toppling the two highest buildings in the city; a third seriously damaged

the Pentagon (五角大楼). The fourth hijacked plane crashed in Pennsylvania. Several thousand people were

killed in the attacks.  

1. During the War of 1812, British forces did the following except that _____.[ ]

A. they captured Detroit

B. they attacked Baltimore and New Orleans

C. they attacked the town of Columbus, N.M.

D. they burned the new capital at Washington, D.C.

2. During the September 11th terrorist attacks, _____.[ ]

A. terrorists hijacked three planes

B. destroyed the Pentagon completely

C. killed six people and injured more than 1,000

D. two planes knocked into New York's World Trade Center

3. The underlined word "toppling" in the last paragraph means _____.[ ]

A. reaching the highest point of

B. causing to fall

C. knocking into

D. building

4. How many foreign attacks mentioned in the passage did the US have? [ ]

A. 5

B. 6

C. 7

D. 8

杆件A端固定，B端固定，其线刚度为i，转动刚度SAB=（）。

A.4i

B.3i

C.I

D.0