Forest fire always (1)_____ by one of two reasons-naturally caused or human-caused. Natural fire is generally (2)_____ by lightning, with a very small percentage (3)_____ by spontaneous combustion of dry fuel such as saw dust and leaves.(4)_____, human-caused fire can happen (5)_____ any number of reasons.
Select the most appropriate option for blank No.3.
Identify the most appropriate option to substitute the underlined segment. If no substitution is required, select No substitution. The shoebill stork can be recognise from its long legs and broad wings.