(a) by reason of the omission of the employer to maintain in good and safe condition any way, works, machinery or plant connected with or used in his trade or business, or by reason of any like omission on the part of any person in the service of the employer who has been entrusted by the employer with the duty of seeing that such way, works machinery or plant are in good and safe condition; or

(b) by reason of the negligence of any person in the service of the employer who has any superintendence entrusted to him, whilst in the exercise of such superintendence; or

(c) by reason of the negligence of any person in the service of the employer to whose orders or directions the workman at the time of the injury was bound to conform and did conform, where the injury resulted from his having so conformed; or

(d) [ by reason of the act or omission of any person in the service of the employer done or made-