(a) That's wrong. To answer this question requires a review of the principles that the courts will apply to decide what a reasonable person would do in the circumstances to prevent foreseeable harm from occurring. The alternative answers remind you that the courts weigh various factors, such as the seriousness of the harm, its likelihood of occurring, and the practicality of preventing it.
In the case study, it would be foreseeable to a reasonable person in Peter's position that faulty electrical connections might cause very serious harm, either to persons or property. A reasonable person would make considerable effort to avoid such serious harm.
How likely was it that the foreseeable harm would actually occur? On the facts it might not be possible to say very likely, but it would be unrealistic to say that the chances were very remote. It is probably fair to say that the chances of serious harm occurring were reasonably likely. This factor would suggest that some effort should be made to prevent the harm from occurring.
How practical would it have been to prevent the harm? On the known facts, carrying out checks would have disclosed the fault. Doing the checks would have cost time and money, but not excessively so. On balance, taking account of the seriousness of the foreseeable harm, and the likelihood of it occurring, the checks should have been carried out.