Fragen über die Beispielsätze mit, und die Definition und Benutzung von "Chosed"

A: No, you can't say "I chosen". Chosen is the past participle and you need a helper verb. You can say "I had chosen..." or "I was chosen" (but this means that you yourself were chosen for something, not that you did the choosing), but you can't use chosen alone as a verb.
For the same reason, "I had chose" is incorrect. With the perfect tense, you have to use the participle. "I had chosen".
Correct sentences are:
"I had chosen the wrong side."
"I was chosen to be the leader."
"I chose the wrong side."
"I have chosen the wrong side."
"I have to choose a side."