Dear Yongshan,

Your score in Exam 2 is 72 out of 100

Everything was right except

#4: wrong answser wrong way
:-10 points

#7(d): wrong way 
:-3 points

#8 : wrong answer, partially wrong way.
You did |r(t)|dt instead of |r'(t)|dt
: -5 points

#9: did not do
:-10 points

Best wishes,

  Dr. Z.