To encourage an open information exchange, we will invite ________ and overseas scholars and experts to give talks on present and future developments in some technical fields.
This new kind of chemicals will help keep the air, soil and water________ from pollution.
Barack Obama has taken personal blame ________ the security failures which led ________ the attempt to blow up a plane on Christmas Day.
―Look! What a mistake! Why? ―Sorry, I _________ on it.
My father didn’t have to say anything. I knew he was upset from his ________.
Cao Cao’s tomb is reported ________ in China, which attracts nationwide attention.