An economy experiences a rise in business confidence, leading to an initial increase in investment of £15 billion£15 \text{ billion}£15 billion. This injection results in a cumulative increase in national income of £45 billion£45 \text{ billion}£45 billion. In response to this rapid growth in national output, firms expand their productive capacity by purchasing new machinery worth £8 billion£8 \text{ billion}£8 billion.

Which row in the table below correctly identifies the economic phenomena responsible for the £45 billion£45 \text{ billion}£45 billion rise in national income and the subsequent £8 billion£8 \text{ billion}£8 billion investment in machinery?

£45 billion rise in national income£8 billion investment in machineryAThe accelerator principleThe multiplier effectBThe multiplier effectThe accelerator principleCThe wealth effectThe multiplier effectDThe multiplier effectThe crowding-out effect\begin{array}{|c|c|c|} \hline & \text{\textbf{£45 billion rise in national income}} & \text{\textbf{£8 billion investment in machinery}} \\ \hline \text{A} & \text{The accelerator principle} & \text{The multiplier effect} \\ \hline \text{B} & \text{The multiplier effect} & \text{The accelerator principle} \\ \hline \text{C} & \text{The wealth effect} & \text{The multiplier effect} \\ \hline \text{D} & \text{The multiplier effect} & \text{The crowding-out effect} \\ \hline \end{array}ABCD​£45 billion rise in national incomeThe accelerator principleThe multiplier effectThe wealth effectThe multiplier effect​£8 billion investment in machineryThe multiplier effectThe accelerator principleThe multiplier effectThe crowding-out effect​​