Understanding the concept of "מצוה" in S'char shabbos.
Planting or Throwing Pits on the Ground;
Dried-out Trees, Fruits, Branches, Alfalfa and Bean Sprouts. Putting an Aravah into Water;
The Halachas of Shabbos When תִּשְׁעָה בְּאָב Falls Out on Motzi Shabbos;