Translation:The dolphin is an intelligent and friendly animal.
Would you please decide whether you wanted "thong minh" to be translated as intelligent, smart or clever. When I put in clever it is wrong, in another sentence I put in intelligent and it was wrong (correct was clever)....
Do you not need "Những" before "Cá heo". Những to indicate plurality, so:
The dolphins are an intelligent and friendly animal.
Maybe, it dosen't sound as natural as The Dolphin is an.....