The two questions 1 & 2 at the lower right refer to the group of terpenes shown on the left. Some of these natural products are readily disconnected into isopentane building blocks. Some cannot, because of alkyl shifts in the late stages of their biosynthesis. The acyclic terpenes may be divided into head-to-tail linked isoprenoids, and those that are not joined in that manner. Enter appropriate letters from A through I in each answer box. If no structure fits the description enter the letter X.