Как все наверное знают отличить Present Perfect и Past simple не всегда легко..особенно если нет слов-маркеров.

Поэтому прошу помощи..Мне задали написать диалог,но меня интересует вот эти две части..

B:Then where have you been?

A:Oh,nowhere.I wanted to go to America two years ago,but now i don't want to go there.

B:Why?

A:I understood,that my wish is impossible,so i refused of it. 

И 2-я

B:Have you heard some interesting news?

A:No.

B:I heard,that Brian flunked his exam last week. 

A:Why did he flunk the exam?

B:He lost his homework,so he didn't repeat a topic.

Правильно ли я все указала?Если нет то поправьте меня..и объясните мои ошибки,ибо я совсем запуталась между этими временами 

B:Then where have you been? (Present Perfect)

A:Oh, nowhere. I wanted (Past simple) to go to America two years ago,but now i don't want to go there.

B:Why?

A:I understood (Past simple) that my wish is impossible, so i abandoned(Past simple) that idea. 

И 2-я

B:Have you heard some interesting news?(Present Perfect)

A:No.

B:I heard (Past simple) that Brian flunked (Past simple) his exam last week. 

A:Why did (Past simple)he flunk the exam?

B:He lost (Past simple)his homework, so he didn't repeat a topic.(Past simple)