Well, the first thing you have to decide is whether you’re interested in physics or chemistry and biology or sociology or whatever else… some of the less hard sciences or whatever it is, where your interests lie. You have to choose a field and usually people don’t have too much difficulty with that because they say… suppose if they’re very good at mathematics but don’t want to be a mathematician they're more likely to go into… into physics or possibly theoretical chemistry or something, and conversely if they’re not and they’re interested in animals and plants… Jim [Watson] was a bird-watcher originally, that’s how he got interested in biology, for example. They go in for it for just rather general feelings as to what they are generally interested and what they’re good at. And I don’t think many people have a lot of problem with that except sometimes that they… they don’t have a very strong feeling one way or the other and it's not clear under those circumstances they'd be advisable to go and do anything. But, having chosen the field, then it’s partly a matter of… of accident and where you’re accepted at a university and how… and do you work on… and which person… where… where you’re accepted to do research although you have some choice in… in where, you know, in… in choosing. But it's also partly a matter of luck and how you get on with this professor or that professor and which other young men you meet and so on. And that will probably lead you to a… a subfield of work of some kind. How you chose the actual problem, that's almost impossible to describe. It depends on the actual field, what it is and how adventurous you should be or not. It depends… you have to look at your temperament and how much you’re prepared to take risks. It's like asking somebody how should you invest. The first thing you ask is, or one of… or the second thing you ask anyway, how much risk do you want to take? And that would certainly be one of the things you would say here and how… how… have you any degree of financial independence, for example, which means you can take bigger risks? Or lots of other considerations of that sort. So, I don’t know anything… very general rules you can give.