"I think I will stroll tomorrow."
Translation:Я думаю, я буду гуляти завтра.
While the English translation is correct, it sounds stilted. The average American speaker would say: "take a walk". I suspect that would not have been accepted.
That's strange. In English you can put "that" or you can omit it if you wish, the meaning will be the same. But in Ukrainian you need to always put a conjunction! Without it is just two separate things: "I think" and "I will stroll tomorrow"