Is cracks in rocks mechanical or
chemical this is for sience

They are caused by both mechanical and chemical forces.

  i think you forgot to put the options but if your reffering to this question then your answer will be "b"  a. add "to" to the base form to create an adjective.b. when the subject of a sentence is singular, add "–s" to the base form.c. add "–ed" to irregular base forms to form the past participle.d. do not use a base form with plural subjects