1. The panda’s ______ habitat is the bamboo forest.
a. nature b. natural c. naturalized d. naturally
2. Learners can feel very ______ if an exercise is too difficult.
a. courageous b. encouraging c. discouraged d. discouragingly
3. The ______ friendly products are designed not to harm the natural environment.
a. environment b. environmental
c. environmentally d. environmentalism