_____ the past, leaving the sadness behind,___________ you’ll see the door of a new bright world open before you

I don’t like its color. Would you show me_____one

I have some difficulty ______English.

I think ____ of the materials I listened to at thebeginning of the exam ____ easy.

下列各组句子中加横线的词，解释全部正确的是（ ）