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Đáp án cần chọn là: A

$\begin{array}{l}B=\frac{2}{3.5}+\frac{3}{5.8}+\frac{11}{8.19}+\frac{13}{19.32}+\mathrm{...}+\frac{25}{32.57}+\frac{30}{57.87}\\ B=\left(\frac{5-3}{3.5}\right)+\left(\frac{8-5}{5.8}\right)+\mathrm{.....}+\left(\frac{87-57}{57.87}\right)\\ B=\left(\frac{1}{3}-\frac{1}{5}\right)+\left(\frac{1}{5}-\frac{1}{8}\right)+\mathrm{.....}+\left(\frac{1}{57}-\frac{1}{87}\right)\\ B=\frac{1}{3}-\frac{1}{87}=\frac{28}{87}\end{array}$