题目

On a sunny spring morning, a seven-year-old girl was sharpening(削) a beautiful pencil. 8 , the wind was so strong as to blow open the door. The girl stood up to  9  it, but then fell on the floor. The sharpened pencil pierced (刺入) directly into the girl’s chest into her heart, and only a small part of the pencil could be seen. The girl’s mother was so  10  that she dialed the emergency number and put the girl flat on her back. The girl  11  and asked her mother to pull the pencil out of her heart  12  it was particularly painful. The mother hesitated for a while but �如图所示电路，电源电压为6V，电阻R2为10Ω，滑动变阻器R1的最大阻值是20Ω，当滑片P移到a端时，电压表读数是______V，当滑片P移到b端时，电压表读数是_______V。