Identifying "чистый родник" (clean spring) vs. "чистые родники" (clean springs) to practice plural endings.

Resources such as 11book often list answers organized by exercise number for quick reference.

ГДЗ (ответы) Русский язык 4 класс Зеленина

For the 3rd-grade Russian language textbook by (usually published in two parts), the reshebnik (answer key) typically covers the following core thematic blocks. Core Textbook Sections (Parts 1 & 2)