Although his lawyers were________about the case,they couldn't be sure about the final outcome of it. [ ]

A. eager  

B. professional  

C. optimistic  

D. sceptical

氢气、瓦斯、天然气及油系统等易燃、易爆或可能引起人员中毒的系统检修，必须关闭有关截止门后，立即在法兰上加装堵板，并保证严密不漏。