Identify the correct spelling of the noun form meaning 'the act of speaking formally':
答案解析
Core concept: Spelling rules (ei/ie exceptions).
Correct answer: C. 'Speech' follows 'i before e except after c' rule.
Error analysis: A/D use incorrect 'ea'; B is phonetic misspelling.
Memory tip: 'speak' becomes 'speech' with same vowel pattern.
正确答案：C