Which of the following statements regarding growth is incorrect?<br><b>(a)</b> In plants, growth by cell division is seen only up to a certain stage.<br><b>(b)</b> Growth exhibited by non-living objects is by accumulation of material on the surface.<br><b>(c)</b> A multicellular organism grows by cell division.<br><b>(d)</b> Growth in invitro culture of unicellular organisms can be observed by counting the number of cells.