An economic crisis are dangerous not only from an economic point of view, but also from a political viewpoint, as it is often followed by a political crisis.
"An economic crisis": Singular --> "are" is not correct
(A) An economic crisis are dangerous not only from an economic point of view, but also from a political viewpoint, as it is often followed by a political crisis
Correct
(B) Since economic crises are often followed by political crises, they are dangerous not only from an economic point of view, but also from a political viewpoint
"Economic crises": Plural --> "is" is wrong
(C) Economic crises is dangerous not only from an economic point of view, but also from a political viewpoint, as they are often followed by a political crisis
an economic crisis: Singular, are: plural --> Eliminate
(D) Because an economic crisis are often followed by a political crisis, it is dangerous not only from an economic point of view, but also from a political viewpoint
Economic crises : Plural, is: singular
(E) Economic crises is often followed by a political crisis, so it is dangerous not only from an economic point of view, but also from a political viewpoint