Read the passage and fill in the blanks with the proper words：（在空格内填入合适的词，使其内容通顺，每空格限填一词，首字母已给）：7%

What do three hearts，eight arms，and one huge brain add up to？An octopus （章鱼）-a sea （72）a that can do amazing（令人惊奇的） things．
Octopuses are very smart．They can learn new things just like humans．They've even learned a few skills to get themselves out of dangerous situations （情况）．Octopuses don't have teeth or sharp claws （爪子） to protect themselves．（73）I ，they use more clever ways to fool their enemies （敌人）．Octopuses like to hide themselves in the sand．An octopus can change the colour of its skin to make it look like sand．And this colour change happens （74）i less than a minute．（75）A way an octopus can hide is by shooting ink．The ink is like a cloud that hides the octopus．By the time the ink clears，the octopus has swum away．
If an octopus is in （76）d ，it can also make itself look like a sea snake．It will hide itself in the sand，leaving two arms outside．It will change the colour of those arms to match a sea snake．
But what will octopus do if there's no time to hide？It can （77）b off one of its arms．The arm will then change colours and keep moving around in the water to take the enemy（敌人）'s attention away．At the same time，the octopus swims away to safety．Don't worry though．The arm will（78）g back．