hello, can I get some help with these questions?

1A). Some substances, particularly high-melting compounds, give broad, indefinite melting points when the determination is carried out in the usual manner but give sharp, well-defined melting points when the sample is not placed in the bath (or block) until the temperature is about 20 below the melting point of the sub-stance. Suggest an explanation for this behavior.

1B). What properties are' often value-able as aids in the identification of an organic compound?

1C). Name five different natural products of organic origin that lack sharp melting points but soften over a wide temperature range. Are these pure organic compounds or mixtures?