Think of pyrolysis on a sliding scale of severity. Low temperature with slow heating is the mildest condition, and mild conditions do not supply enough energy to fully crack the biomass into small gas molecules or to keep the vapours from recombining and depositing as solid carbon. What remains is largely carbonaceous char, the same product you get from a slow charcoal kiln.
As you push the severity up, either by raising temperature or by shortening how long the vapours sit in the hot zone, the balance of products shifts. Moderate, fast conditions favor liquid bio-oil because vapours are quenched before they crack further. High temperature with longer residence time favors gas because everything keeps breaking down into smaller molecules.
Since the question specifically asks about relatively low temperature, none of the gas-rich or oil-rich outcomes apply, and the correct product is the carbon-rich solid residue.
\[\boxed{\text{Carbonaceous char}}\]