题干

如图所示观察水面波衍射的实验装置,AC和BD是两块挡板AB是一个小孔,O是波源,图中已画出波源所在区域的传播情况,每两条相邻的波纹(图中曲线)之间距离表示一个波长,则对于波经过孔之后的传播情况,下列描述正确的是(   )

①此时能明显观察到波的衍射现象

②如果将孔AB扩大,有可能观察不到明显的衍射现象

③挡板前后波纹及间距离相等

④如果孔的大小不变,使波源频率增大,能明显观察到衍射现象.

A:只有②④

B:只有②

C:只有①②③

D:①②③④

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C

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    Even the hardest days contain lessons that will help you be a better person. Feeling down? Consider these things to remember when you're having a bad day.

    No one promised life would be perfect.

    ____Don't base your happiness on meeting every expectation you set for yourself. It is good to be ambitious, but you'll never be perfect. If you expect otherwise, your life will be filled with disappointments.

    ____

    Trees that are slow to grow bear the best fruit. Don't kid yourself into thinking success will come quickly. It isn't easy to be patient, but anything worth doing requires time____

    Without hard times, you wouldn't appreciate the good ones.

    Strength does not come from winning. Your struggles develop your strengths. When you go through hardships and decide not to give up, that is strength____. It is hard to find much to smile about when you fail, but how else would you improve yourself? If you look at failures as a part of your growing process, you'll stay positive and follow your goals for as long as it takes.

    It's OK to cry sometimes.

    Do not apologize for crying. Without this feeling, we are only robots. Don't be afraid of crying____Instead, it is an acceptable way to let go of your depressed feelings. If you let those feelings build up without release, you'll have a much harder time dealing with them later.

A.Don't get sad if you lose.

B.It isn't a sign of weakness.

C.Success doesn't happen overnight.

D.It's not OK to worry now and then.

E.Don't compare your life with others'.

F.Remember: Rome was not built in a day.

G.If you look for perfection, you'll never be content.