(七)阐述原因
1. The epidemic of … is brought / caused both by … and by…
……的出现是由于……和……造成的。
2. One of the chief causes of… is the fact that …
……的主要原因之一是……
3. The upsurge of … is resulted from two-fold factors ——…
……的出现源于双重因素——……