Based on the text, humus has the following properties: it is a dark coloured amorphous substance; it is highly resistant to microbial action; and it serves as a reservoir of nutrients . Additionally, it is colloidal in nature and undergoes decomposition at an extremely slow rate . Assuming standard statements derived from this text (where typically (a) is dark/amorphous, (b) is resistant, and (e) is reservoir of nutrients), the correct combination is (a), (b), and (e).