请问什么时候应该用being

IT identifies the ten rivers most risk and says some in danger are being lost for ever, while others face massive degradation. Matt Mcgrath reports.

The disease is spread to humans through the bite of mosquitoes infected with malaria parasites, the most dangerous of these being plasmodium falciparum

1 being,表示现在正在被流失，the rivers are lost-> the rivers are being lost.
2 being 是be的“悬垂分词”，“表伴随”， ect...
就像we have 4 roommates, the youngest "coming" from Shanghai.中的coming，
原文中being plasmodium falciparum， 就是the most dangerous of these is plasmodium falciparum.的变形
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being的用法

一 用作现在分词
1 构成状语。
如：Being angry at his question,I made no reply.
2 用于构成被动语态进行时。
如：Being ill,I could not go with you.
3 当动词be作“behave,act”解时，being作为be的进行时可以用来表示临时的行为或表现。
如：The experiment was being made at this time yesterday.
4 与过去分词一起构成后置定语（常含“被动进行”概念）。
如：We must keep a secret of the things being