Explanation:

- The sentence is supposed to convey a continuous action that started in the past and is still ongoing.

- Option 1: since

- "Since" is used correctly to indicate the start of a past event in relation to a present action.

- Option 2: yesterday

- "Yesterday" works here to specify the time when the action began.

- Option 3: Elina is

- "Elina is" refers to the subject and helping verb, but the tense isn't right. "Has been traveling" would be correct for ongoing actions that started in the past.

- Correct Answer " Elina has been"

- Option 4: travelling

- "Travelling" (British spelling) refers to the ongoing action, which is appropriate but needs a different helping verb for accuracy.