下列方程中，是一元二次方程的有个． ①ax2+bx+c=0；②2x（x﹣3）=2x2+1；③x2=4；④（2x）2=（x﹣1）2⑤ x2−3xx =2x2．

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下列方程中，是一元二次方程的有（）个．

①ax²+bx+c=0；②2x（x﹣3）=2x²+1；③x²=4；④（2x）²=（x﹣1）²⑤

−

=2x²．

A：4

B：3

C：2

D：1

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What to Bring When Visiting Lijiang of Yunnan
Welcome to Lijiang. Lijiang is a nice place to visit. If you visit Lijiang, you’d better do as the following.

Needs	Reasons
1. Hat and sunglasses	The Lijiang’s sun can be quite shiny even during winter, so remember to bring a hat and sunglasses.
2. Raincoat or umbrella	It’s hard for us to know Lijiang’s weather, so it is necessary to bring an umbrella or a raincoat to Lijiang, even if it is sunny.
3. Water	A day in Lijiang you may be very thirsty, so make sure that you bring a bottle of water with you.
4. Camera	There will be lots of chances to take photos on your visit to Lijiang, so make sure to bring your camera. Don’t forget to bring more batteries so that you won’t miss anything!
5. Watch	There are many sights and gift shops in Lijiang. Bring a watch, so you can arrange (安排) your time.

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