Part C of the sentence has the error. 'Can' and 'able to' are not used together in the sentence as both indicate 'ability' and 'capacity', which makes their usage superfluous.
Hence, option (c) is correct.
The correct sentence is: Across the world, corals vary widely, both in the temperatures they experience and they can withstand high temperatures without becoming stressed or dying.
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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