Fill each blank with one suitable word by choosing A, B or C.

People need air to breathe. In order to keep us healthy, we need (31) _____ air. However, nowadays, (32) _____ lot of things in our lives create harmful gasses and make the air dirty, like factories, cars and motobikes. Air (33) ______ is one of the worldwide alarming issues nowadays. It causes not only (34) ______ problems in people but also in plants and animals. It’s our responsibility to keep the air (35) _____.