Look at this from the purpose of the terrace rather than trying to memorise a number in isolation. A level (table top) bench terrace is used for irrigated field crops planted across the whole strip, so it needs a wide flat top, typically 3 to 6 metres, to fit multiple crop rows and allow machinery to move.
An orchard terrace exists purely to hold one line of fruit trees running along the contour. Since only a single tree row sits on each bench, the strip does not need to be nearly as wide as a crop terrace. Soil conservation design guidance for deep soils gives about 2 metres as the practical top width for such an orchard bench, wide enough for the tree's root zone and a safe working margin, but no wider than necessary.
Checking the alternatives, 3 metres suits a field crop terrace rather than an orchard row, and 0.5 metre or 1 metre would be too tight for a mature tree's base and root spread on a stable terrace edge. So 2 metres is the width that fits the actual function of an orchard bench terrace.
\[\boxed{2\ \text{m}}\]