Both words refer to keeping an action or process going without interruption. With continue, the subject can persist in its own movement (I continued to dance) or keep something else going (They continued the conversation), whereas sustain is limited to the latter case and always takes a noun as its direct object (How did you manage to sustain the conversation?). In terms of meaning, continue emphasizes an activity that is kept up, while sustain implies keeping something in existence or making it last: sustain economic growth; sustain the momentum or pace.
Change refers to an instance of something becoming different than it was or being replaced by something new: a change in leadership; changes in the environment. Vicissitude refers to one of a succession of changes or alterations in the state, form, or condition of something over time. The most familiar use of vicissitude is in the plural, as in the vicissitudes of life. In this sense, the vicissitudes—of life, history, politics, fortune, love, or the market—suggests something like “the twists and turns” and “ups and downs” that characterize the course of any of these major human affairs when considered in its entirety. When we use “change” as a mass noun, as in “Change is constant,” this approaches the meaning of vicissitudes, but is more abstract and general. Vicissitudes evokes the particularity and number of the changes we weather.
Both words are used to describe intense or forcefully expressed emotions or opinions. Strong suggests felt or expressed with some degree of intensity: strong feelings; a strong objection, but strong’s wide range of application tends to dilute its precision and strength in these contexts. Vehement, which comes from a Latin word meaning “forceful” or “violent,” suggests something felt or expressed with intense passion. Vehement is not limited to a negative meaning (a vehement expression of his faith) but it does tend to be used most frequently for oppositional feelings and utterances: vehement protest, a vehement denial, vehement opposition.