 Okay, so let's do this one. It says, rank the following set of substituents in order of priority according to the common engulfed pre-log sequence rules, okay? So, we've got a compound here, and sometimes it's easier if you write out all of the functional. Okay, so hopefully you can see this is a carboxylic acid. Let's just write, I know you noticed that. Let's just write it out so we remember that double bond there. Same thing with this, this is an aldehyde, okay? So, let's write that out so we remember that double bond there. So, it's going to come into play in a little bit, okay? So, now we've got to ask ourselves, what are the highest priority? I didn't look at your answers to know if you were right or not, okay? I just want to tell everybody, okay? So, when we left, we'll always say, what's big is oxygen, oxygen, carbon, or carbon? Well, oxygen's bigger than carbon, so we've got to look at these two substituents here. So, what's bigger? Carbon or hydrogen? Carbon is bigger, okay? So, this is going to be number one, okay? So, now, remember, what's bigger, oxygen or carbon? Oxygen's bigger, so we say, that's two, like that, okay? Now, we've got to ask ourselves, which one of these is bigger? Well, carbon or carbon, they're the same. Now, we go to the double oxygen, double oxygen, they're the same, okay? This one has an oxygen, that one has a hydrogen. So, this one is going to be three, that one's going to be four, okay? Does that make sense? Okay, that's probably what you have, right? Okay, any other questions on that one? Okay, one more.