Give the correct form of the words in brackets to complete the following passage. Unwanted Visitors

Loss of habitat poses the single greatest threat, endangering indigenous. The second largest threat to native flora and fauna would have to be the (36. INTRODUCE)………..of alien species into an environment other than their own. Alien species are able to cause such cataclysmic damage because they are usually more (37. SUCCESS)………..in competing for food. They introduce diseases to which the local inhabitants do not possess (38. IMMUNE)………... Interbreeding has caused the destruction of entire species because the first hybrid generation will eventually (39. PLACE)………..the parent stock. Hybrid individuals tend to possess greater vigour and will therefore compete more (40. EFFECT)………..with the remaining pure stock. Their offspring may also be infertile, resulting in the (41. POPULATE)………..of an entire species because of a reduction in the number of breeding animals. The (42. FORM)………..of guidelines has been called on to exclude non-native wildlife, contain it where it has a foothold, and eliminate it if possible. The principles call for border controls, (43. CAUTION)………..in international trade and technical and financial (44. ASSIST)………..help poor countries detect and combat (45. INVADE)………...

(CPE Use of English 1 for the Revised Cambridge Proficiency Examination Student's Book)