An apostrophe is used when you want to do one of the following: show possession, when changing a single noun to its plural form and when you are using contractions, or contracted words, like it and is. In this particular case, we have two cases in which we need to use apostrophes. The first is the use of the last name of two subjects. This last name is, in its singular form, Smith, but because we are talking about more than one (plural), we need to change the singular word into its plural form. To do this, we add the apostrophe after the H and add an s. This shows the plural form. Also, we have a contracted word, it and is. The correct way to show the contraction is by using an apostrophe between the original word (it) and to signify the presence of is adjoined to it, we add an apostrophe and we add the "s" after it. This is why the correct answer is A.
The biggest issue with this is that the first sentence is run-on, you should consider breaking it into smaller sentences, maybe by getting rid of the "and" after describing the mother, replacing it with a period and letting the father get a sentence of his own. Also, you could try "-on how happy the Railway family is. The story also uses detail on how nice the parents are-" something along those lines, just to break the run-on sentence?
This is minor, but at the end "creates a sense of perfection, by describing their house-" the comma before by isn't necessary, and can either be deleted, or you can rephrase like "a sense of perfection. The story does this by describing-"
I hope this helps! <span />
