Here's why:
* Spelling: The "o" in "solid" is followed by a consonant and a silent "d". This is a common pattern for long vowel sounds in English.
* Pronunciation: You pronounce the "o" in "solid" with a long "o" sound, like the "o" in "go" or "toe".
Short vowel sounds are typically associated with single vowels, while long vowel sounds can be represented by single vowels followed by a consonant and a silent letter, or by two vowels together.