You _______be too careful when you are driving.

More subway lines ______ to make travelling easy in Beijing in the coming years.

an, as well as Mary’s, sounds original. But thecompany, I think, won’t agree to __________ of them, for they are unrealistic.

I ______ peaceful countryside ______ noisycities while my sister prefers _____ in the modern cities.

下列句中加点的熟语，不能用括号中的四字格成语替换的一句是    （    ）