请问qǐng wèn:always followed by question sentence.Because literary meaning of this phase is: please( can i ) ask. Eg: qǐng wèn, qù fēi jī chǎng zěn me zǒu? ( Excuse me, how can I get to the airport?)
对不起duì bù qǐ: can be followed by a question as well as statement. The literary meaning is : sorry ( to disturb ) Eg: duì bù qǐ, wǒ yào qù xǐ shǒu jiān.(Excuse me, I'm going to the bathroom)