单项选择题

A.电源开关-加热器开关-坩埚开关-籽晶开关
B.电源开关-坩埚开关-加热器开关-籽晶开关
C.电源开关-籽晶开关-坩埚开关-加热器开关
D.籽晶开关-坩埚开关-加热器开关-电源开关