单项选择题
Which of the listed conditions can be considered as the single greatest cause of accidents?（）
A.Speed B.Excessive knowledge or skill C.Human error D.Excitement
单项选择题 Which of the following must be eliminated to prevent accidents?（）
单项选择题 Which of the following is not a recommended safe practice?（）
单项选择题 When required to work where there may be explosive gases, you should use tools which are （）
