Work done by a constant force $\vec{F}$ on a body that undergoes a displacement $\vec{d}$ is given by the dot product: $W = \vec{F} \cdot \vec{d} = | \vec{F}| |\vec{d}| \cos \theta$, where $\theta$ is the angle between the force and displacement vectors. Work is negative when $\cos \theta$ is negative. This occurs when the angle $\theta$ is between 90° and 270° (exclusive of 90° and 270° where work is zero). Let's examine the options: A) Angle is 135°. $\cos 135° = -1/\sqrt{2}$. Since $\cos \theta$ is negative, the work done is negative. B) Angle is 0° (same direction) or 180° (opposite direction). If $ \theta=0°$, $\cos 0° = 1$, work is positive. If $ \theta=180°$, $\cos 180° = -1$, work is negative. So, parallel force and displacement can result in negative work (if opposite directions), but doesn't always. C) Angle is 90°. $\cos 90° = 0$. Work is zero. D) Angle is 45°. $\cos 45° = 1/\sqrt{2}$. Since $\cos \theta$ is positive, work is positive. Option A is the only situation listed that guarantees the work done by the applied force is negative.