Concept:After the verb "let", the object must be followed by the base form of the verb, which is called the bare infinitive.
Explanation:The emboldened part uses "left", which is the past tense form and is incorrect here.
The correct pattern is: let + object + base verb.
Phrase I uses "going", which is not the base form.
Phrase II uses "went", which is the past tense form.
Phrase III uses "leave", which is the base form of the verb.
So only phrase III is grammatically correct.
The corrected sentence is: "Real Madrid is ready to let Gareth Bale leave for a cut-price fee of
£22 million as they continue to try and free up their hefty wage bill."
Thus, only phrase III can replace the emboldened phrase correctly.
Answer:Option A — Only III