This is an importnant piece of r_____ into the causes on cancer

Is this an egg? this is an easy this is an Is this an eye? Is this an umbrella this is an is ,an,book,english,this This is an[ ][amaze] story. This is an Africa tiger . this is less of an This is an ）tiger. This is an English pen is this an apple an orange__an egg This is ----- egg.can Ieat------ egg?an,an an,the This is an orange and that is an( ) this is an order.中is 和an要连读吗? this is an empty box=this box is not this is an apple.改成复数形式