Fill in the blanks in the following passage with proper words.

According to a recent study, the same worldwide drought could have been【A1】______ for the decline of two ancient civilizations on opposite sides of the globe.

A research team, 【A2】______ by Germany National Research Center for Geosciences in Potsdam， found a【A3】______ caused by weaker summer monsoon rains might have【A4】______ to the downfall of the Tang Dynasty in China and the Mayan civilization in Mexico.

The scientists【A5】______ sediments from Huguangyan Lake in Zhanjiang of South China’ s Guangdong Province and found that Asian summer monsoon rains were【A6】______ during the 8thand 9th【A7】______ , during which the Tang Dynasty faded from glory.

The hypothesis stemming from geological analysis are【A8】______by some of China’ s【A9】______ documents, which record a sudden drop in temperature in middle-late Dynasty, according to Fang Xiuqi, a researcher of China’ s disaster history at the Beijing Normal 【A10】______ .

Fang said Chinese history of the past 2, 000【A11】______ records three extremely frigid periods， one of which【A12】______ in the late 8th century. “There is some interesting evidence about stronger winds at that time in literature, ” he said. For example, most of the【A13】______ written during the early periods of the【A14】______ were about plum blossoms, an indicator of warm【A15】______, while those completed later were mainly odes to the cold. “Journals about cold weather also increased after around AD 750, during which a big【A16】______ began, ” Fang said

Historians【A17】______the rebellion as a turning point in the Tang era a prime period of China’ s civilization which suffered more insurrections before finally dying out.

The German researchers have also found the【A18】______pattern in sediments from the Cariaco basin off the Venezuelan coast, indicating a similar drought might have hit nearby Mexico and【A19】______about the downfall of the【A20】______civilization in the late 8th century.