Concept:
Use
past perfect tense to show an action completed before another past action.
Step 1: Identify tense of main clause.
\[
{“manager arrived”} \Rightarrow {simple past}
\]
Step 2: Action before this should be in past perfect.
\[
{Past Perfect} = {had + past participle}
\]
Step 3: Evaluate options.
- (A) has already started $\times$ present perfect
- (B) had already started \checkmark correct (past perfect)
- (C) is already starting $\times$ present continuous
- (D) was already starting $\times$ past continuous (not completed action)
Hence, the correct answer is had already started.