标点符号问题，求助各位任者侠客

Iljiajia

As well as heat and light, the Sun is the source of a continuous stream of atomic particles known as
the solar wind.
(A) As well as heat and light, the Sun is the source of a continuous stream
(B) Besides heat and light, also the Sun is the source of a continuous stream
(C) Besides heat and light, the Sun is also the source of a continuous streaming
(D) The Sun is the source not only of heat and light, but also of a continuous stream
(E) The Sun is the source of not only heat and light but, as well, of a continuous streaming

答案是D，我是排除后选出来的，但唯一不理解为什么but also前面多个“，”呢？？
这不是第一次遇到这种问题了，请各路神通不吝赐教，多谢多谢

Iljiajia

终于与捧场的了，谢谢，关键有不少题符号也是考点，所以不得不多留个神

dajiahaoh

我也选D，不要纠结逗号

Iljiajia

似乎没有共鸣，自己顶一下