Choose the odd one out.

The odd one out is C, IO. The other options, AE, AI, EI, and OU, are all digraphs, which are two letters that represent a single sound. The letter combination IO does not represent a single sound in English. It can be used to represent two different sounds: the long “i” sound as in “ice” or the long “o” sound as in “go.”

A digraph is a pair of letters that represent a single sound. Some common digraphs in English include:

• ch: as in “chip”
• sh: as in “ship”
• th: as in “thin”
• wh: as in “white”
• ea: as in “eat”
• ai: as in “rain”
• ei: as in “eight”
• oi: as in “oil”
• ou: as in “out”

Digraphs are important because they allow us to represent a wider range of sounds than we could with just the 26 letters of the alphabet.