演讲 

Pinyin: yǎn jiǎng 
Meaning：(Give) a speech or lecture  
Sentence：这位著名的经济学家给我们做了一次演讲。The famous economist gave us a speech.

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演： 

Pinyin: yǎn
Meaning: Act; deduce; develop; evolve; perform; practice
Radical: 氵
Stokes: 14
Traditional: 演
Common words/Phrase:
演变 [yǎn biàn] 【develop; evolve】
表演 [biǎo yǎn] 【perform; play; act; put on】 
推演 [tuī yǎn] 【deduce】
天演 [tiān yǎn] 【natural evolution】
演示 [yǎn shì] 【to demonstrate】

讲： 

Pinyin: jiǎng
Meaning: Speech; to talk; to speak; to tell; to explain
Radical: 讠
Stokes: 6
Traditional: 講
Common words/Phrase:
讲座 [jiǎng zuò] 【a course of lectures】 
讲解 [jiǎng jiě] 【to explain】
讲义 [jiǎng yì] 【teaching materials】
讲师 [jiǎng shī] 【lecturer; instructor】
讲述 [jiǎng shù] 【talk ab0ut】