The footbridge is an alternative for ______ to cross the road. A. spectators B. cyclists C. pedestrians D. passers-by E. motorists

A footbridge is specifically designed for people who are walking to cross a road or obstacle. C. pedestrians are people walking. The answer is $\boxed{\text{C}}$

Obesity is primarily caused by consuming an excess of calories, often from foods high in fat and sugar. Doctors frequently advise reducing the intake of fatty foods to manage weight and prevent obesity. B. fatty foods are a major contributor to obesity. The answer is $\boxed{\text{B}}$

School management often warns students against putting unauthorized items on walls, especially those that can deface property or are difficult to remove. Stickers are a common item students might post that fits this description. C. stickers are often prohibited on school walls. The answer is $\boxed{\text{C}}$

Smoking is highly addictive, meaning it causes a physical or psychological dependence. The most appropriate word to describe someone's relationship with smoking, especially if they engage in it regularly, is addicted. A. addicted means having a compulsive physiological or psychological need for a habit-forming substance. The answer is $\boxed{\text{A}}$