Final answer:
The actus reus for section 18 wounding is 'unlawfully causing harm,' where the offender must have specific intent to inflict grievous bodily harm or prevent lawful apprehension.
Step-by-step explanation:
The actus reus for section 18 wounding, under UK law, refers to the 'guilty act' component of a criminal offense and for section 18 is specifically the unlawfully causing harm. Section 18 falls under the Offences Against the Person Act 1861 and is considered the most serious form of non-fatal bodily harm due to the necessity for a specific intent to inflict grievous bodily harm (GBH) or to resist or prevent the lawful apprehension or detainer of any person. Therefore, the correct answer is d) Unlawfully causing harm, considering that the defendant must be proven to have acted with specific intent to cause serious injury, an element that goes beyond negligence or recklessness.