CDs are susceptible to damage during handling and from environmental exposure. Pits are much closer to the label side of a disc, enabling defects and contaminants on the clear side to be out of focus during playback. Consequently, CDs are more likely to suffer damage on the label side of the disc. Scratches on the clear side can be repaired by refilling them with similar refractive plastic or by careful polishing. The edges of CDs are sometimes incompletely sealed, allowing gases and liquids to corrode the metal reflective layer and to interfere with the focus of the laser on the pits. The fungus Geotrichum candidum, found in Belize, has been found to consume the polycarbonate plastic and aluminium found in CDs.
How are scratches on a CD fixed?
refilling them with similar refractive plastic or by careful polishing

Some critics express the opinion that it is only from the mid-19th century, and especially in the 20th century, that the score began to hold such a high significance. Previously, improvisation (in preludes, cadenzas and ornaments), rhythmic flexibility (e.g., tempo rubato), improvisatory deviation from the score and oral tradition of playing was integral to the style. Yet in the 20th century, this oral tradition and passing on of stylistic features within classical music disappeared. Instead, musicians tend to use just the score to play music. Yet, even with the score providing the key elements of the music, there is considerable controversy about how to perform the works. Some of this controversy relates to the fact that this score-centric approach has led to performances that emphasize metrically strict block-rhythms (just as the music is notated in the score).
When did oral tradition disappear?
the 20th century

At the beginning of the Three Kingdoms era (220280 CE), Zhejiang was home to the warlords Yan Baihu and Wang Lang prior to their defeat by Sun Ce and Sun Quan, who eventually established the Kingdom of Wu. Despite the removal of their court from Kuaiji to Jianye (present-day Nanjing), they continued development of the region and benefitted from influxes of refugees fleeing the turmoil in northern China. Industrial kilns were established and trade reached as far as Manchuria and Funan (south Vietnam).
What was home to the warlord Yan Baihu?
Zhejiang