Translating 'thanks to' with a Japanese Clause

The problem is the word class after thanks to. 'Thanks to' is a prepositional phrase, so it needs a noun phrase as its object, not a full clause with a subject and a past-tense verb. In 'the teacher praised our presentation,' 'the teacher' is the subject and 'praised' is the verb, so the whole clause cannot be the object of 'to.' Two repairs are: (1) use a possessive plus gerund: 'Thanks to the teacher's praising our presentation'; (2) use a noun clause with 'the fact that': 'Thanks to the fact that the teacher praised our presentation.' A third option is to change the connector to a conjunction: 'Because the teacher praised our presentation, everyone...' That is also correct, but it loses the positive 'thanks to' nuance. The student should notice that Japanese 「おかげで」 can be translated as 'thanks to' only when the following element is a noun phrase; otherwise, 'because' or 'the fact that' is often smoother.

'Could have confidence' is grammatically possible, but it sounds like a general ability or a hypothetical possibility. The Japanese 「自信を持てた」 presents a result that actually happened: the students reached a state of confidence because of the teacher's praise. 'Was able to gain' makes that result concrete and dynamic. 'Gain confidence' is also a strong collocation; it describes the change from less confidence to more confidence. 'Have confidence' describes a state, which is less precise here because the sentence is about what the praise caused. The respectful 「くださった」 is not fully translatable, but 'the teacher's praising' keeps the action neutral; if the student wants to show respect, 'kindly praised' is possible, though not required by the answer key. The main lesson is to match English aspect to the Japanese result: use 'was able to gain' when the sentence reports an achieved change, not just a potential.