Anthropologists have discovered that fear,happiness,sadness and surprise are universally reflected in facial expressions

2 .因为主语为名词复数.
3.universally,reflect和facial依次译为普遍的,反映和相同的.因为你太相信金山词霸了,而且犯了翻译界的一忌,那就是逐字翻译.
第1个疑问与第4个疑问我在此一并回答.
Anthropologists have discovered that fear,happiness,sadness and surprise are universally reflected in facial expressions.
此句貌似是that引导的宾语从句,其实非也.此句为that引导的同谓语宾语.简单来说Anthropologists have discovered （that）that reflected in facial expressions.这句话你能理解吗?括号里的that才是宾语从句,为什么将其省略呢?因为为了避免重复.其中that充当的是代词,译为“那个”,那个是哪个呢?就是that后面的同谓语fear,happiness,sadness and surprise are universally .
如果理解上还是有问题,那再给你举个例子.
i find it difficult to finish it on time.
此句中的it相当于上句的that,区别是it在此句中是形式宾语,而that是同谓语.