Select the option that can be used as a one-word substitute for the underlined group of words.
After my father passed away, I used to look at a series of stars, trying to find the unknown.
Rearrange the parts of the sentence in correct order.
The nanostructures on the
P. with added, or "doped," iron and phosphor
Q. surface made of nickel selenide
R. offers the high performance and stability
S. that are needed for industrial-scale electrolysis