对于任意的非零实数m，关于x的方程x²-4x-m²=0根的情况是（　　）

A．有两个正实数根

B．有两个负实数根

C．有一个正实数根，一个负实数根

D．没有实数根

在下面对话的空白处，填入适当的句子，使对话意思完整，每空填一句。

提示：李雷到一家商店想买一台电脑。

A: Shop assistant         B: Li Lei

A: (1) _________________________?

B: Yes, I want to buy a computer.

A: What kind of computer would you like?

B: (2) _________________________. Because of I have no much money.

A: OK. What are this one? It's cheap.

B: Oh, it looks nice. (3) __________________________?

A: It costs 3988 yuan.

B: OK. (4) ________________________. Here's the money.

A: (5) __________________________. Here's your change (零钱).

B: Good-bye.

A: Bye-bye.