如图，在▱ABCD中，点M为CD的中点，且DC=2AD，则AM与BM的夹角的度数为（　　　）

$S_n$ 为等差数列 $\left\{a_n\right\}$ 的前n项和，且 $a_n\text{=}1，S_7=28.$ 记 $b_n\text{=}\lg a_n$ ，其中 $x$ 表示不超过x的最大整数，如 $0.9\text{=0}，\lg 99\text{=1}$ .

阅读短文，判断正误。

    I have a happy family. There are five people in my family. My grandpa and my grandma are very old, they like watching TV very much. My father is a doctor,  and my mother is a nurse. They work hard. I'm a student in Grade Three. I love my family.