我认为,最简单的说 that代指不同的事物 it代指相同的事物 这个goal是相同的事物, 比如 Mammal's lungs are usually larger than that of bird. 没问题,因为这两种肺是不一样的,哺乳动物肺和鸟肺 再比如: This exam is as hard for as it is for Tom. 考试是一样的,所以不能说as that is for Tom.
A: in the like + noun construction, the comparison is made between the noun and the SUBJECT of the main clause, choice A clearly refers "that" to goal, yet the subject of the main clause is "owning and living in a freestanding house", thereby makes a comparison between a "goal" and the "content of a goal", this is incorrect.
Apart from this, "that" vs. "it" has been clearly explained above.