(2013·合肥一中二模)I don't know who invented ________ iphone，but I think it is ________ useful invention.

A．the；a B．the；the C．an；the D．an；a

(2013·南阳两校联考)Keeping a diary is ________ good habit，by which you'll make ________ great progress in writing.

A．a；a B．a；/ C．the；a D．the；/

(2013·咸阳二模)—Have you seen ________ pen？I left it here this morning.

—Is it ________ black one？I found it in the corner.

A．a；the B．the；the C．a；a D．the；a

(2013·昆明二模)The operation is ________ success and the patient is now out of ________ danger.

A．a；the B．a；/ C．/；the D．/；/

(2013·西安一中月考)As ________ unemployment is very high at the moment，it's very difficult for people to find ________ work.

A．the；/ B．/；/ C．the；a D．an；the

(2013·无锡一模)The education of ________ young is always ________ hot and serious topic.

A．/；/ B．the；a C．/；the D．the；/

(2013·泰安一中月考)—John has put forward ________ most challenging question for us to answer.

—Yes，it really is.I have never heard ________ harder one.

A．the；/ B．/；the C．the；the D．a；a

(2013·泰州二模)In the market，vegetables are sold by ________ kilogram，I mean，by ________ weight.

A．the；/ B．/；/ C．the；the D．/；the

(2013·嘉兴一中月考)Many people agree that ________ knowledge of English is a must in ________ international trade today.

A．the；an B．a；/ C．the；the D．/；the

Everything comes with ________ price；there is no such ________ thing as a free lunch in the world.

A．a；a B．the；/ C．the；a D．a；/