Решение:
Нужно вставить сравнительную степень прилагательных, указанных в скобках, в предложения:
- Elena wants to climb the lower (low) wall.
- Walking is safer (safe) than kayaking.
- Cycling is easier (easy) than climbing.
- The higher wall is more exciting (exciting) than the lower wall.
- Elena is better (good) at climbing than Tom.
Ответ: 1. lower; 2. safer; 3. easier; 4. more exciting; 5. better.