【Question 8】
A store sells a product with the following schemes:
A. First increase the price by $10 \%$, then decrease it by $10 \%$
B. First decrease the price by $10 \%$, then increase it by $10 \%$
C. First increase the price by $20 \%$, then decrease it by $20 \%$
D. First increase the price by $30 \%$, then decrease it by $30 \%$

Among these four sales schemes, the one with the lowest price is scheme $\qquad$
【Analysis and Solution】Economic problem.

Plan $A$: The final price is the original $(1+10\%) \times(1-10\%)=(1+0.1) \times(1-0.1)=1^{2}-0.1^{2}$; Plan $B$: The final price is the original $(1-10\%) \times(1+10\%)=(1-0.1) \times(1+0.1)=1^{2}-0.1^{2}$; Plan $C$: The final price is the original $(1+20\%) \times(1-20\%)=(1+0.2) \times(1-0.2)=1^{2}-0.2^{2}$; Plan $D$: The final price is the original $(1+30\%) \times(1-30\%)=(1+0.3) \times(1-0.3)=1^{2}-0.3^{2}$; Since $0.1^{2}<0.2^{2}<0.3^{2}$, we have $1^{2}-0.1^{2}>1^{2}-0.2^{2}>1^{2}-0.3^{2}$; Therefore, among these four sales plans, the lowest price is in Plan $D$.