Questions

I am black gold i.e charcoal. It is black when it is not used and when using it is red due to fire and when used it is in grey color as it becomes ash. 

"The moon smiled at me" is the example of personification in the given options.

Personification is a technique in which we give objects human traits like emotions, gestures, speech,... by using metaphor. 

Here moon is an object which cannot smile but using metaphor sense, we gave that sense to it.

Nucleus serves as the control center for cell metabolism and reproduction.

Sigmoid colon or pelvic colon is a curved, S-shaped portion of the large intestine which is closest to the rectum and anus.

* It helps to transports fecal matter from the descending colon to the rectum and anus.

* It is the final segment of the colon.

The one word substitution for Of outstanding significance is monumental which has a meaning of great in importance, in size or any such characteristic.