在任务、挑战、困难面前，一句“我能行”，会给自己莫大的力量。“我能行”是（  ）
①一种信念、一种力量，能鼓舞人们绕过困难，躲过挑战，等待成功
②自信的表现
③每个成功者都具有的品质
④深信自己一定能实现所追求目标的心态

    My grandpa often goes for a____in the park. He never loses his way.

    But yesterday, a police car____him home. A police officer told (告诉) me that my grandpa was____in the park.

    When the police officer went away, I asked grandpa, "What's____with you today?" "Nothing, I just felt____and I didn't want to walk home. So I called the police and they took me home."

皮肤癌变一般发生于哪一层细胞的什么期(　　)