Scientific experiments by students without the teachers’ instructions can be dangerous.
A. carry out
B. carrying out
C. carried out
D. carrying
网友回答
A. carry out
B. carrying out
(答案→)C. carried out
D. carrying
解析：考查非谓语动词experiments与carry out为动宾关系要用过去分词作定语。句意：学生没有老师指导做科学实验有可能有危险。