Learners can feel very ______ if an exercise is too difficult.

The ______ friendly products are designed not to harm the natural environment.

The waste from the chemical factory is extremely ______.

People are destroying the air by adding ______ to it.

14 percent of primate species are highly ______.

The ______ of old buildings should be taken into consideration.

You have to be aware of the damage humans are doing to quicken the ______ of wildlife.

Animal ______ supporters gathered to protest' against hunting.

The main threat to the ______ of these creatures comes from their loss of habitat