The correct option is A Attached unbranched filament
Ulothrix commonly attached to the bed of fresh water streams and rivers. It also grows on wet cliffs, damp soil, or stagnant water. It is a genus of filamentous green algae, generally found in fresh and marine water. Its cells are normally as broad as they are long, and they thrive in the low temperatures of spring and winter. They become attached to surfaces by a modified holdfast cell.