点P（4，-2）与圆x2+y2=4上任一点连线的中点轨迹方程是______．

丝瓜为雌雄同株异花植物，将刚萌发的丝瓜种子浸泡在下 * * 种溶液中24小时，然后种植，比较雄花与雌花平均数并求出性别比如下表，分析下表数据后得出的结论中，不正确的是

A．甲液对丝瓜花性别分化影响不大

B．乙液较利于雌花的形成

C．丙液对丝瓜花性别分化影响不大

D．丁液有利于雄花的形成

用括号中动词的适当形式填空

1. I _____ (not visit) Shanghai World Expo last summer.

2. — ______ Nancy____ (go) to New York City last weekend?

    —Yes, she____ (go) there with her parents.

3. —What ______ you ______ (buy) in Beijing?

    —I ______ (buy) nothing.

4. —How ______ (be) the beaches there?

    —Beautiful.

5. Last Sunday we had great fun ______ (swim) in the lake.

如图所示，下列操作中正确的是[ ]

A.

B.

C.

D.

基础代谢率的正常值是()

A．-4%～+4%

B．-6%～+6%

C．-10%～+10%

D．-8%～+8%

E．-12%～+12%

正常标准成本