Why is article 1 section 8 clause 18 called the elastic clause

Does anyone know the answers to the australia and the pacific test? here is one of the questions: "which is the correct order of events related to the history of australia and new zealand? place the earliest event at the top and the last event at the bottom." 1. australia and new zealand become dominions. 2. world war 1 occurs. 3. australia and new zealand become independent countries. 4. british recognizes australia and new zealand as equals to britain under the british crown. , i need the correct order down below. i need to submit fast and do not waste my time.