'Or tell you that you should try to' would replace the highlighted phrase because usually 'nor' is preceded by 'neither' which is not the case, instead positive alternatives are being talked about so 'or' would be correct. Option (b) can be eliminated because a base verb would be correct to use after the modal verb 'will' like the base verb 'warn' as modal verbs are always followed by the base verb, but 'told' is the past tense/participle. Option (c) is eliminated because 'but' is used to add contrast which is not the requirement as the sentence is about two alternative choices. Option (d) is incorrect because the context of the sentence is altered by adding the negative word 'cannot'.
Hence, option (a) is correct.
NOTE:
Modal verb: A verb used with another verb to express an idea such as possibility that is not expressed by the main verb. The modal verbs in English are "can," "could," "may," "might," "must," "ought," "shall," "should," "will," and "would." They do not change their form (spelling) and they have no infinitive or participle (past/present). Example: I can speak Spanish. Here 'can' expresses the ability of the person to speak (main verb) Spanish. This ability cannot be expressed by the main verb 'speak'.
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