The correct option is
A To
Option B- To is used to indicate direction, purpose, limit, attachment,
comparing. The given sentence indicates a cause. Thus 'to' is the
correct answer.
Option A- Of is used to indicate possession, relation, substance, cause
or about. As it does not fit the meaning of the sentence correctly, it
is incorrect.
Option C- At is used to indicate a point of time or place, state, direction. age or occupation, degree. Thus it is incorrect.
Option D- In is used to indicate place, time, occupation, state, subject
or matter. As it does not bring out the meaning of the sentence it is
incorrect.