水平角观测中，盘左起始方向OA的水平度盘读数为358°12＇15＂，终了方向OB的对应读数为154°18＇19＂，则AOB前半测回角值为： （）

A:156°06＇04＂ B:-156°06＇04＂ C:203°53＇56＂ D:-203°53＇56＂

已知预应力锚索的最佳下倾角，对锚固段为β1=ψ-α，对自由段为某滑坡采用预应力锚索治理，其滑动面内摩擦角ψ=18°，滑动面倾角α=27°，方案设计中锚固段长度为自由段长度的1/2，问依据现行铁路规范全锚索的最佳下倾角β计算值为以下哪一数值（）

A:9° B:12° C:15° D:18°

如右图所示，在△ABC中，已知AB=AC，AM=AN，∠BAN=30°，∠MNC的度数是（）。

A:15° B:20° C:25° D:30°

Passage Five
Temperatures on December 12
City High Low
Cleveland .................. 37° 31°
Columbia, S. C ............ 60° 27°
Columbus, Ohio ............ 41° 34°
Dallas .................... 81° 50°
Dayton. ................... 41° 33°
Decatur ................... 39° 30°
Denver .................... 49° 33°
Des Moines ................ 34° 27°
Detroit ................... 37° 28°
Dubuque ................... 30° 23°
Duluth .................... 19° 10°
Eau Claire ................ 24° 19°
El Paso ................... 79° 36°
Evansville ................ 52° 36°
Fairbanks ................. -31° -40°
Fargo ..................... 17° -2°
Flint ..................... 31° 26°
Flagstaff ................. 56° 31°
Great Falls ............... 14° 3°
Grand Rapids .............. 33° 26°
Green Ray ................. 24° 20°

What was the high temperature in Columbus, Ohio on December 12（）

A:81°. B:50°. C:41°. D:60°.

Passage Five
Temperatures on December 12
City High Low
Cleveland .................. 37° 31°
Columbia, S. C ............ 60° 27°
Columbus, Ohio ............ 41° 34°
Dallas .................... 81° 50°
Dayton. ................... 41° 33°
Decatur ................... 39° 30°
Denver .................... 49° 33°
Des Moines ................ 34° 27°
Detroit ................... 37° 28°
Dubuque ................... 30° 23°
Duluth .................... 19° 10°
Eau Claire ................ 24° 19°
El Paso ................... 79° 36°
Evansville ................ 52° 36°
Fairbanks ................. -31° -40°
Fargo ..................... 17° -2°
Flint ..................... 31° 26°
Flagstaff ................. 56° 31°
Great Falls ............... 14° 3°
Grand Rapids .............. 33° 26°
Green Ray ................. 24° 20°

What was low temperature in Flagstaff on this day（）

A:26°. B:-2°. C:3°. D:31°.

Passage Five Temperatures on December 12 City High Low Cleveland .................. 37° 31° Columbia, S. C ............ 60° 27° Columbus, Ohio ............ 41° 34° Dallas .................... 81° 50° Dayton. ................... 41° 33° Decatur ................... 39° 30° Denver .................... 49° 33° Des Moines ................ 34° 27° Detroit ................... 37° 28° Dubuque ................... 30° 23° Duluth .................... 19° 10° Eau Claire ................ 24° 19° El Paso ................... 79° 36° Evansville ................ 52° 36° Fairbanks ................. -31° -40° Fargo ..................... 17° -2° Flint ..................... 31° 26° Flagstaff ................. 56° 31° Great Falls ............... 14° 3° Grand Rapids .............. 33° 26° Green Ray ................. 24° 20°

What was low temperature in Flagstaff on this day（）

A:26°. B:-2°. C:3°. D:31°.

Passage Five Temperatures on December 12 City High Low Cleveland .................. 37° 31° Columbia, S. C ............ 60° 27° Columbus, Ohio ............ 41° 34° Dallas .................... 81° 50° Dayton. ................... 41° 33° Decatur ................... 39° 30° Denver .................... 49° 33° Des Moines ................ 34° 27° Detroit ................... 37° 28° Dubuque ................... 30° 23° Duluth .................... 19° 10° Eau Claire ................ 24° 19° El Paso ................... 79° 36° Evansville ................ 52° 36° Fairbanks ................. -31° -40° Fargo ..................... 17° -2° Flint ..................... 31° 26° Flagstaff ................. 56° 31° Great Falls ............... 14° 3° Grand Rapids .............. 33° 26° Green Ray ................. 24° 20°

What was the high temperature in Columbus, Ohio on December 12（）

A:81°. B:50°. C:41°. D:60°.

如下图所示，在△ABC中，已知AB＝AC，AM＝AN，∠BAN＝30°。问∠MNC的度数是多少（）

A:15° B:20° C:25° D:30°