人们在探索微观物质的历程中，相继发现原子核、电子、中子和质子．这些微粒中不带电的是（　　）

How to protect your teeth
____ . The first of twenty being to grow when you are over six months old. The second set of thirty-two grows from the age of six until you are about twenty-one years old.
____ , you must drink plenty of milk and eat greens.
____ . Then little food will be left on or between them to cause decay(导致蛀牙). Make sure that you turn the brush and go up and down as well as brushing side ways. Use dental floss(牙线)to make sure all food is removed from in between each tooth, if you cannot brush your teeth after eating, raise them with water, or eat an apple or a carrot.
____ . If there is a hole in a tooth, he or she will fill it. If you do not have it filled, then the hole will grow larger. When a hole grows too big,____ . It is better to keep all your second set of teeth for as long as possible. Filling a gap where a tooth has come out with a kind of bridge and using a false tooth costs a lot of money.

已知双曲线 $\frac{x^2}{a^2}\text{-}\frac{y^2}{b^2}\text{=}1\left(a＞0\text{,}b＞0\right)$ 与圆 $x^2+y^2\text{=}{c}^2\left(c\text{=}\sqrt{a^2+b^2}\right)$ 交于A、B、C、D四点，若四边形ABCD是正方形，则双曲线的离心率是（  ）

下列是对课文的理解和赏析，正确的一项是（     ）

为了探究音调与什么因素有关，小明设计了下面几个实验，如图所示，你认为不能够完成探究目的的是(   )