1. Cactus can also become thorns and thick stems, which is related to the environment 2. How does the shadow under the sun change in a day? It is longer in the morning, then shorter, shortest at noon, and then longer. It is longest when the sun is about to set in the West. The direction is () 3. Soil is a mixture of sand, pebbles, clay, humus, water, air, () 4. Bicycle chain and gear are used () method to reduce friction

1. Cactus can also become thorns and thick stems, which is related to the environment 2. How does the shadow under the sun change in a day? It is longer in the morning, then shorter, shortest at noon, and then longer. It is longest when the sun is about to set in the West. The direction is () 3. Soil is a mixture of sand, pebbles, clay, humus, water, air, () 4. Bicycle chain and gear are used () method to reduce friction

1, reduce transpiration, dry
2, East
3. Minerals
4. Rolling friction