Điền vào chỗ trống:
 
extinct , alien plants, unchecked, destroyed, agricultural, balance, die out, vegetation

Human activity is a primary reason why many species are now _______ and many more are endangered. The problem is that habitats are being ________ not by one single event, but by a series of actions. One example is when people introduce ________ or animals to a new environment where they have no natural predators. This risks disturbing the ecological ________ in the area and kills native species. Humans also damage the Earth by cutting down forests for development and _________ purposes. If this trend continues _________, the future of the planet will be a grim one indeed.
                                                            ( adapted from Reading for the Real Word 1 )