如图，在菱形ABCD中，AB=BD，点E、F分别在BC、CD上，且BE=CF，连接BF、DE交于点M，延长ED到H使DH=BM，连接AM，AH，则以下四个结论：

①△BDF≌△DCE；②∠BMD=120°；③△AMH是等边三角形；④S_{四边形ABMD}= $\frac{\sqrt{3}}{4}$ AM²．

其中正确结论的个数是（　　）

阅读下面的短文，根据短文内容完成句子。每空词数不限。

    This is a song millions of Americans will hear this New Year's Eve. It is called “Auld Lang Syne(《友谊地久天长》)”. It is the traditional music played during the New Year's celebration. Auld Lang Syne is an old Scottish poem. It tells about the need to remember old friends.

    The words “auld lang syne” means “old long since”. No one knows who wrote the poem first. However, a version (译本) by Scottish poet Robert Burns was published in 1796. The words and music we know today first appeared in a songbook three years later.

    The song is played in the United States mainly on New Year's Eve. The version you are hearing today is by the Washington Saxophone Quartet. As we end our program with “Auld Lang Syne”, I would like to wish all of our radio friends a very Happy New Year! This is Buddy Thomas.

已知向量 $a=\left(-k,4\right)$ ， $b=\left(k,k+3\right)$ ，且 $\overrightarrow{a}$ 与 $\overrightarrow{b}$ 的夹角为锐角，则实数k的取值范围是（请写成区间形式）____．

《尚书大传》说：“古者诸侯始受封，必有采地：百里诸侯以三十里，七十里诸侯以二十里，五十里诸侯以十五里。其后子孙虽有罪黜，其采地不黜，使子孙贤者守之世世，以祠其始受封之人，此之谓兴灭国，继绝世。”材料反映了（    ）