Grateful acknowledgement is made to the following sources:
Every effort has been made to contact copyright owners. If any have been inadvertently overlooked, the publishers will be pleased to make the necessary arrangements at the first opportunity.
219574: Figure 1 top left: © erstudiostok / 123 Royalty Free
219577: Figure 1 top right: © Iakov Filimonov / 123 Royalty Free
219571: Figure 1 middle left: © Cathy Yeulet / 123 Royalty Free
219579: Figure 1 middle right: © Anna Bizon / 123 Royalty Free
219576: Figure 1 bottom: © William Perugini / 123 Royalty Free
219684: Figure 21 left: © dotshock / 123 Royalty Free
219596: Figure 21 right: © Cathy Yeulet / 123 Royalty Free
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