A:k<﹣1
B:k≤﹣1
C:k>2
D:k≥2
下列命题的逆命题为真命题的是( )
He felt very happy, because he ______ the exam.
如图,PA,PB是⊙O的切线,CD切⊙O于E,PA=6,则△PDC的周长为____