答案：$\frac{1}{7} + \frac{3}{7} = \frac{4}{7}$
$\frac{7}{9} - \frac{5}{9} = \frac{2}{9}$
$\frac{3}{4} + \frac{1}{4} = 1$
$\frac{3}{4} - \frac{1}{4} = \frac{2}{4} = \frac{1}{2}$
$\frac{5}{6} + \frac{5}{6} = \frac{10}{6} = \frac{5}{3}$
$\frac{7}{12} + \frac{7}{12} = \frac{14}{12} = \frac{7}{6}$
$\frac{11}{12} - \frac{1}{12} = \frac{10}{12} = \frac{5}{6}$
$\frac{6}{7} - \frac{3}{7} = \frac{3}{7}$
$\frac{3}{8} + \frac{3}{8} = \frac{6}{8} = \frac{3}{4}$
$\frac{4}{15} + \frac{8}{15} = \frac{12}{15} = \frac{4}{5}$
$\frac{9}{35} + \frac{6}{35} = \frac{15}{35} = \frac{3}{7}$
$\frac{9}{10} - \frac{3}{10} = \frac{6}{10} = \frac{3}{5}$

答案：$\frac{1}{2} + \frac{1}{3} = \frac{3}{6} + \frac{2}{6} = \frac{5}{6}$
$\frac{1}{7} + \frac{1}{5} = \frac{5}{35} + \frac{7}{35} = \frac{12}{35}$
$\frac{1}{4} + \frac{2}{5} = \frac{5}{20} + \frac{8}{20} = \frac{13}{20}$
$\frac{1}{9} + \frac{1}{3} = \frac{1}{9} + \frac{3}{9} = \frac{4}{9}$
$\frac{1}{5} + \frac{1}{10} = \frac{2}{10} + \frac{1}{10} = \frac{3}{10}$
$\frac{7}{8} - \frac{1}{8} = \frac{6}{8} = \frac{3}{4}$
$\frac{2}{7} + \frac{1}{14} = \frac{4}{14} + \frac{1}{14} = \frac{5}{14}$
$\frac{4}{5} + \frac{1}{4} = \frac{16}{20} + \frac{5}{20} = \frac{21}{20}$
$\frac{1}{18} + \frac{2}{3} = \frac{1}{18} + \frac{12}{18} = \frac{13}{18}$
$\frac{1}{21} + \frac{2}{3} = \frac{1}{21} + \frac{14}{21} = \frac{15}{21} = \frac{5}{7}$
$\frac{1}{2} + \frac{3}{13} = \frac{13}{26} + \frac{6}{26} = \frac{19}{26}$
$\frac{3}{4} - \frac{3}{9} = \frac{27}{36} - \frac{12}{36} = \frac{15}{36} = \frac{5}{12}$
$\frac{1}{2} - \frac{1}{17} = \frac{17}{34} - \frac{2}{34} = \frac{15}{34}$
$\frac{1}{2} + \frac{1}{17} = \frac{17}{34} + \frac{2}{34} = \frac{19}{34}$
$1 - \frac{4}{11} = \frac{11}{11} - \frac{4}{11} = \frac{7}{11}$

答案：①
$\begin{aligned}\frac{1}{10} + \frac{3}{10} + \frac{7}{10} + \frac{9}{10} &= \frac{1 + 3+7 + 9}{10} \\&= \frac{(1+9)+(3 + 7)}{10}\\&= \frac{10 + 10}{10}\\&= \frac{20}{10}\\&= 2\end{aligned}$
②
$\begin{aligned}\frac{1}{13} + \frac{2}{13} + \frac{3}{13} + ··· + \frac{11}{13} + \frac{12}{13}&=\frac{1 + 2+3+···+11 + 12}{13}\\ \mathrm{因为}1+12 = 13,2 + 11 = 13,3+10 = 13,4 + 9 = 13,5+8 = 13,6+7 = 13\mathrm{共}6\mathrm{组},\\所以原式=\frac{(1 + 12)+(2 + 11)+(3 + 10)+(4 + 9)+(5 + 8)+(6 + 7)}{13}\\=\frac{13×6}{13}\\&= 6\end{aligned}$
答案依次填入：$2$；$6$；需要努力处填（根据实际情况，此处假设填“×”表示错误相关不做具体评价内容，按要求只给答案相关），本题答案相关框应填： （第一个空）$2$；（第二个空）$6$；基本过关处填（√ ）；非常出色处填（ ）。 （基本过关处打√表示评价，非常出色处空白）。