Concept:Use "elder" for a sister or brother in a family.
Solution:"Senior" refers to rank or position, not family relations.
"Older" is the general comparative of "old" (for people and things, e.g. "older than me").
"Matured" means fully grown or developed.
"Elder" is the special form used before a noun to show who was born first in a family (elder sister, elder brother, elder son).
So we say: "She is my elder sister."
Key point: In everyday speech "my older sister" is also heard, but in standard (and examination) English the word for seniority within a family is "elder".
Answer:Option B (elder)