If you are running the Dopey (marathon and 5k included within), then if you're predicting corral D/E for the marathon you have a VERY high probability you are in corral A for the 5k/10k. However, if you individually signed up for the 5k and marathon, then your corral placement in both is not related to each other. But in all likelihood if you put down a 27ish minute 5k, I'd believe you're likely in corral A or B (but I don't know the 5k corrals timing specifically for individual sign-ups).