Why is "que" necessary in this sentence? Wouldn't that be the difference between "I think THAT he is going to remember" and "I think he is going to remember", which is the sentence DL is asking to be translated?
In Portuguese you can't omit the relative pronouns!
What about the reflexive pronoun? I used "se" but it suggested that I could have also left it out. is it really optional in Brazil?
Yes, it is opitional.
In a previous example, I think Paulenrique was the one who said that anytime the word "that" is optional in English, it is required in Portuguese. So far, that's worked well for me.
Why is it lembrar instead of lembra?
It just told me that: Eu acho que vai lembrar is wrong
You can't omit the pronoun in this sentence because it could be "ele, ela or você".
Why is "Eu acho que ele irá lembrar." a correct solution? It is the future of ir... shouldn't be subjunctive because of eu acho expressing opinion? Eu acho que ele vá lembrar." No?