They started off at about 5 o’clock in the morning . They should       there by now .

A．arrive

B．have been arriving

C．have arrived

D．be arriving

下列细胞中，参与蠕虫免疫的白细胞为

A．中性粒细胞

B．嗜酸性粒细胞

C．嗜碱性粒细胞

D．T淋巴细胞

E．B淋巴细胞