Большой русско-английский фразеологический словарь
Я ДУМАЮ!
•Я ДУМАЮ!coll
[sent;Invar; fixedWO]
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⇒(used to express one's emphatic agreement with the interlocutor's statement or affirmative response to a question) definitely, certainly:
-(but) of course!;
-naturally!;
-what do you think!;
-you said it!;
-I'll say!
♦ "Это ведь настоящий мех?" - "Я думаю! Посмотри на цену!" "This is real fur, isn't it?" "But of course! Look at the price!"