顺次连接对角线相等的四边形的各边中点，所形成的四边形是（　　）

Beethoven is a very____ （著名的）musician .
I'm____ （紧张的）out because I can't find the way home.
My mother often____ (担心)about my father's health..
She likes to s____  e-mails at school.
Lily is very t____ , she'd like to have some water.

下列式子成立的是（　　）