Risk factors
Family history. Because a family history of Graves' disease is a known risk factor, there is likely a gene or genes that can make a person more susceptible to the disorder.
Sex. ...
Age. ...
Other autoimmune disorders. ...
Emotional or physical stress. ...
Pregnancy. ...
Smoking.
B)
Explanation:
The correct answer is option two.
An infinitive phrase consists of an infinitive verb, and can be followed by a complement or a modifier, which is usually an adverb.
In the sentence above, the infinitive phrase comes before a complement "variety and interest to their writing."