Answer: Option A
Answer: (a)Let us consider all the options one by one. (a) has ‘is the cause of’ in place of ‘are caused of’ and hence it cannot be a correct option. Now, Let us move on to option (b). When we replace the phrase given in bold by the phrase given in option (b), the sentence becomes "........... factory are caused by of workers........." How can we use two preposition ‘by’ and ‘of’ together? Therefore, this option also is ruled out. On replacement by option (c) the given sentence becomes grammatically correct and meaningful. Hence we must go with this option.