Liǎng ge shǎngshēng zì lián zài yìqǐ shí, qián yí ge yào dúchéng yángpíng.
When two third-tone syllables come together, the first one is read as a second tone.
Tips
mistakes
上 is read shǎng in this word, not shàng. Many speakers now say shàngshēng, but dictionaries keep shǎngshēng.
history
Middle Chinese had four tones: 平声 (level), 上声 (rising), 去声 (departing) and 入声 (entering). In classical verse the last three together are 仄, 'oblique', set against the level 平.