The error was in not performing a 180° bond rotation to remove the zigzag conformation.

The error was in the specified direction of viewing the line-angle drawing. It should be viewed at the top left of the C3-C4 bond.

The error was in the given line angle drawing of L-Threose. One hydroxyl group should be on a wedge, while the other should be on a dash.

The error was in the given line-angle drawing of L-Threose. Both hydroxyl groups should be on a dash.