Fill in the blanks using the correct word given in brackets:
$(i)$ All circles are $........$ (congruent,similar)
$(ii)$ All squares are $.........$ (similar,congruent)
$(iii)$ All $.........$ triangles are similar. (isosceles,equilateral)
$(iv)$ Two polygons of the same number of sides are similar,if $(a)$ their corresponding angles are $......$ and $(b)$ their corresponding sides are $......$ (equal,proportional)

(A) $(i)$ All circles have the same shape but not necessarily the same size,therefore they are similar.
$(ii)$ All squares have the same shape (all angles are $90^{\circ}$ and sides are in the same ratio),therefore they are similar.
$(iii)$ All equilateral triangles have angles of $60^{\circ}$ and equal side ratios,therefore they are similar.
$(iv)$ Two polygons are similar if $(a)$ their corresponding angles are equal and $(b)$ their corresponding sides are proportional.