5. I'm on your side.
我是站在你这边的。
还能这样说：
I will support you.
I stand by your side.
谚语：
The grass is greener on the other side.
这山看着那山高。

6. He's efficient.
他很能干。
还能这样说：
He is capable.
He has a lot on the ball.
应用解析：
efficient in 在……有成效；
be fully efficient 充分发挥效力的；
be highly efficient 高效率的

7. He's very vague.
他是个难以捉摸的人。
还能这样说：
He is difficult to understand.
He isn't very clear.
应用解析：
one's very thoughts 正是某人的想法；
the very reverse of the truth 与事实完全相反

8. He's faithful.
他是守信用的人。
还能这样说：
He is a man of his word.
He stands to his word.
应用解析：
words and deeds 言与行；
word came that 有消息传来说