content_image/907738.jpg content_image/907739.jpg content_image/907740.jpg
<img src='content_image/907738.jpg'>

-continued 

<img src='content_image/907739.jpg'>

Illustrative examples of the recurring units having formula (C) are given below, but not limited thereto. 

<img src='content_image/907740.jpg'>

-continued 

