HI!

Standing in line at the post office, little Margarita greets each new patron with a cheery ``Hi!''; but when she gets nary a nod in return her assurance begins to diminish. When it's her mother's turn, Margarita tries once more, now in a whisper, and the postal clerk comes through with a hearty ``Hi!'' and a smile- -plus a wave and a farewell ``Bye!'' Scott's tribute to persistence (essentially a simpler rendition of her perennial favorite, Sam) is warm, sweet, and minimalist. Coalson's soft, bright watercolor illustrations depict an appealingly doe-eyed tot and a realistically motley mixture of other folks at the P.O. Try this for the toddler group. (Picture book. 2-6)