It is important to provide evidence of using a variety of reliable resources. Use the online Reference Generator available through the Portal to create your citations. Make sure you alphabetically sort them afterwards.
A sample bibliography for 3 resources suggested on this page would look like:
Biome 2019. Britannica School. Retrieved 13 March 2019, from https://school.eb.com.au/levels/middle/article/biome/317523
Biomes 2019, BBC, London, accessed 13 March 2019, <https://www.bbc.com/bitesize/guides/zh2p34j/revision/1>.
Richardson, G 2009, Ecosystems, Weigl, New York.