It is these poisonous products ________
问题:
It is these poisonous products ________ can cause the symptoms of the flu, such as headache and aching muscles.
A.who
B.that
C.how
D.what
It is these poisonous products ________ can cause the symptoms of the flu, such as headache and aching muscles.
A.who
B.that
C.how
D.what