Here are the boxes with fewer objects:
a)
The left box has 5 stars.
The right box has 3 moons.
Since 3<5, the box with the moons has fewer objects.
Rightbox(moons)✓
b)
The left box has 2 wavy lines.
The right box has 5 straight lines.
Since 2<5, the box with the wavy lines has fewer objects.
Leftbox(wavylines)✓
c)
The left box has 7 arrows.
The right box has 4 spirals.
Since 4<7, the box with the spirals has fewer objects.
Rightbox(spirals)✓
That's 2 down. 3 left today — send the next one.