Given the context provided, the goal is to express a reflection on your doubts about being able to complete a triathlon event that you ended up participating in. Here’s an analysis of each option in relation to the context provided:

A) "I thought I would never be able to get through it."

• This option is grammatically correct. It effectively communicates that during the event or before it, you doubted your ability to complete it. It’s a straightforward way to reflect on your earlier doubts.

B) "I never thought I would be able to get through it."

• This option is also grammatically correct. It suggests a consistent disbelief in your ability to complete the event, up until you proved yourself wrong by actually participating. This option subtly implies a longer period of doubt.

C) "I thought I would have never gotten through it."

• This option is awkward and less clear. The use of the future perfect tense ("would have never gotten") is not appropriate in this context. It tries to reflect on a past perspective about a future outcome, which doesn�t fit well here.

D) "I thought I would have never been able to get through it."

• Similar to option C, this sentence is complex and grammatically awkward. The construction "would have never been able" complicates the expression of doubt and is not commonly used in this type of reflection.

Given these analyses, A) "I thought I would never be able to get through it." and B) "I never thought I would be able to get through it." are the correct options. They both clearly and effectively convey the sense of doubt about completing the triathlon.

Which to choose between A and B depends on the nuance you want:

• A suggests a specific moment or period where you doubted your ability.
• B suggests a more ongoing, persistent doubt over time.