Option D, aerate well, in a couple days you will have enough yeast to handle the extra sugar you will be adding then.
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If you ended up with 6.5 gal of 1.060 wort, that's about 60% efficiency by my math. What would your typical efficiency be for a smaller beer? Lauter efficiency for that mash (it sounds like you were batch sparging) would be ~80%, so your conversion efficiency is in the 75% range.
Have you calibrated your thermometer(s) and hydrometer(s)? Did you check mash pH? Generally, for conversion efficiency to suffer, either the temperature or the pH has to be out of range.
No matter what, I'm thinking you may have some volume measurement error, since 10 gal - 18 lb * 0.12 gal/lb = 7.84 gal. Unless you're mechanically squeezing the mash dry, you shouldn't have been able to get 8+ gal out of it.