情景选择。

1. 现在是早晨，Sarah去Mr Black那儿看病，她该说：            [ ]

A. Good morning, Mr Black.

B. Good aftemoon, Mr Black

C. What's your name?

D. Who are you?

2. 看过病后，Mr Black告诉Sarah多喝水，Mr Black应该说：           [ ]

A. I like water, Sarah.

B. Have some water, Sarah.

C. I like juice, Sarah.

D. Have some milk, Sarah.

3. Sarah问Mr Black:“我能吃热狗吗？”她该说：         [ ]

A. Thank you.

B. I like hot dog.

C. Have some hot dogs.

D. Can I have a hot dog?

令A=1×2+2×3+3×4+…+98×99+99×100且B=1²+2²+3²+…+98²+99²．那么A-B=______．