A manufacturing project has a schedule performance index $($SPI$)$ of $0\mathrm{.}89$ and a cost performance index $($CPI$)$ of $0\mathrm{.}91.$ Generally, what is the most likely explanation for why this occurred?a$.$A critical path activity took longer and needed more labor hours to complete.b$.$The scope was changed.c$.$Additional equipment needed to be purchased.d$.$A supplier went out of business, and a new one needed to be found.