During the scientific experiment, Mr. Chen carefully poured the water into the tube, with my classmates ____ beside to see what would happen.

A．were standing

B．stood

C．standing

D．to stand

肉瘤是指( )

A．来自上皮组织的恶性肿瘤
B．来自间叶组织的恶性肿瘤
C．来自肌肉组织的肿瘤
D．来自平滑肌的肿癌
E．来自胚胎组织的肿癌