Which of the following is a characteristic of a horizontally opposed engine?

A horizontally opposed engine, commonly referred to as a "flat" engine, features a design where the cylinders are arranged horizontally on either side of a central crankshaft. This arrangement allows the opposing cylinders to balance each other, reducing vibrations and enhancing smooth operation. The flat configuration often leads to a lower center of gravity, which can improve the aircraft's stability and handling characteristics.

In contrast, a V-shape design would imply that the cylinders are arranged in a "V" formation, which is not characteristic of horizontally opposed engines. Inline cylinders would suggest a single line or row configuration, which again is not applicable to horizontally opposed engines. A two-row configuration typically refers to radial engines, where cylinders are arranged in a circular pattern around the crankshaft, rather than on opposite sides of the crankshaft as in horizontally opposed engines. Thus, the flat engine configuration is distinct and accurately defines the characteristic of a horizontally opposed engine.