In this question, you are being asked to choose the correct auxiliary verb to complete the request '18. ______ you help me with this?'.
Let's look at the options given:
i) can
'Can' is used to express ability or possibility. In a request, 'can' suggests asking someone if they are able to help.
ii) must
'Must' is not typically used to make requests. It is used to express necessity or obligation.
iii) will
'Will' is used to express a future action or willingness. In a request, 'will' is used to ask if someone is willing to help.
iv) may
'May' is used to ask for permission. However, in this context, it wouldn’t be used for a request for help.
Given these explanations, the most appropriate words for a request are 'can' and 'will'. They both work, but 'can' is more commonly used for informal requests suggesting ability. Thus, the best choice to complete the request is:
'Can you help me with this?'
So, the correct answer is: i) can.