C

The formula for induced e.m.f (electromotive force) in a coil due to the change in magnetic flux is given by Faraday's law of electromagnetic induction. According to this law:
e = -rac{dlux}{dt} where η is the induced emf and lux is the magnetic flux, which can be expressed as lux = A imes B (where A is the area of the coil and B is the magnetic field). The negative sign indicates the direction of the induced emf as per Lenz's law, which states that the induced emf will work in the direction to oppose the change in flux. Hence, we can express the induced emf as:
e = -rac{d}{dt}(A imes B). This matches with option C. Therefore, the correct answer is C.