I suspect it depends on what type of Christian they are. The stakes are highest for fundamentalist, 'sola scriptura', Protestants because if you believe that the Bible is the inerrant word of God then any flaw or discrepancy in the text means the whole lot must be discarded. Hence there is a temptation to defend every last point and cling doggedly to every shaky defence.
There will also be those, of all churches, who just lack the skills for debate, and find it easier to repeat mantras unquestioningly.
There are also Christians out there who are intelligent, will engage with the question and will attempt to give thoughtful answers. They may even be prepared to give ground on certain points in a debate. But there comes a point, where even people like this will have to fall back on lines such as 'It's a mystery' or 'We just have to accept this on faith'. I can see how this may seem like evasiveness but at times it is the only honest answer to give.
The best way I can explain this last point is by analogy with science. There are some scientific facts and concepts which are just as inexplicable as anything in religion. How a electron can be in two places at once, or what energy really is, for instance, are impossible to explain to a layman and perhaps even the best scientists cannot really understand these questions. But the fact that a scientist cannot explain wave-partical duality or quantum entanglement to me in any deep way doesn't mean that he is being evasive, or that I should reject the totality of scientific knowledge. There are times when we just have to have the humility to accept that not all things are within our understanding.