3a2b3c的系数是（ ），次数是（ ）；πR2的系数是（ ），次数是（ ）。
3；6；π；2
He was sentenced to death ____ what he has stolen from the bank. [ ]
A. that
B. since
C. because
D. because of
That art center is _______ used to be a factory, ______ millions of tractors were produced.
A．what; where
B．where; where
C．what; which
D．where; which
