The worker witnessed ________ seen the accused near the scene of the crime.[ ]

A. to have  

B. to having

C. for having  

D. having

请说出下列事实的原因：

(1)用棕色瓶盛AgNO₃；__________________

(2)用铁质容器盛浓H₂SO₄；_________________

(3)液Cl₂盛子钢瓶；_________________

(4)盛汽油的容器不能用胶塞。_________________