对磁场和磁感线，下列说法正确的是

A．只要导体做切割磁感线运动，导体中就会产生感应电流

B．地磁场的南极在地理北极附近

C．发电机是根据电磁感应现象制成的

D．在磁场中，小磁针静止时北极所指的方向为该点的磁场方向

As it is used in the passage, the word "photosphere'' (Line 2, Para. 2) means ______.

A．a scarlet gaseous envelope surrounding the Sun

B．the luminous envelope of gas surrounding the Sun

C．the mixture of gasses that surrounds any planet or star

D．the luminous irregular envelope of highly ionized gas outside the chromospheres of the Sun