Grammaire anglaise : environnement et verbes

Read the following sentences about the environment and fill in the blanks using the correct form of the verbs in brackets. Context: We want to reduce our carbon footprint ($CO_2$) to protect Earth. 1. If we ________ (recycle) more, we ________ (save) energy. 2. We ________ (should / plant) more trees to absorb $CO_2$. 3. People ________ (not / throw) plastic into the ocean yesterday, but they still do it today.