In financial statement analysis, expressing all financial statement items as a percentage of base-year amounts is called

A is the correct one...

Answer A is correct

Horizontal common-size analysis is the correct answer.

A. Horizontal

A. Horizontal common-size analysis.

answer 

A. Horizontal common

Correct answer is Horizontal common size analysis

its called ratio analysis- it could be in form of Horizontal /vertical common size analysis, 

A is correct because several years of data compared with base year.

Horizental Analysis is right answer.