Studies show that young people with higher-than-average blood pressure and their families have a history of high blood pressure
are more likely than others to develop a severe form of the condition.
Since the meaning is easy to understand, let’s begin the error analysis
: In this sentence the verb “have a history…” does not make sense with the subject “young people with higher-than-average blood pressure and their families”. The position of this clause makes the entire structure ungrammatical. As such, the verb “are” is left without any subject that leads to fragment error. POE:
(A) and their families have a history of high blood pressure: Incorrect
for the reason stated above.
(B) whose families have a history of high blood pressure: Correct.
Notice that “whose” is a relative pronoun, a noun modifier that is modifying a little far away noun “young people”. This is so because the prepositional phrase preceding “whose” cannot be placed anywhere else in the sentence without affecting the meaning. Hence, the relative pronoun can jump over “with higher-than-average blood pressure” to modify “young people”.
To know, how this modification is possible, read the article by clicking on the following link:noun-modifiers-can-modify-slightly-far-away-noun-135868.html
(C) and a history of high blood pressure runs in the family: Incorrect.
Same fragment error and ungrammatical structure issue as in choice A.
(D) whose families have a history of high blood pressure running in them: Incorrect.
The verb-ing modifier “running” is modifying the preceding noun entity “history of high blood pressure”, meaning that the “history of high blood pressure” run in the “young people and their family”. This is illogical.
(E) with a history of high blood pressure running in their family: Incorrect.
Use of “running” seems to suggest that “a history” runs in their family. This modification does not make sense.
Hope this helps.