Select the most appropriate pair of words to fill in the blanks in th…

The correct answer is Option (1) → had submitted, started

Past perfect and simple past:

• When two past actions are put in order, the earlier action takes the past perfect (had + past participle) and the later action takes the simple past.
• This sentence:
  • The researcher submitted her findings first → "had submitted".
  • The conference started later → "started".
  • "Before" introduces the later action, so the simple past follows it.
• Complete sentence: The researcher had submitted her findings before the conference started.

Why the Other Options are Incorrect?

Option 2: has submitted, has started — Incorrect.

• The present perfect links a past action to the present. It does not show which of two past actions came first.
• "Before the conference has started" is not natural English.
  Example: She has submitted her report, so she is free now.

Option 3: submitted, start — Incorrect.

• "Before the conference start" is wrong: the singular subject "conference" needs "starts" or "started".
• A past verb is needed to match "submitted".
  Example: She submitted her findings yesterday.

Option 4: submit, starts — Incorrect.

• The singular subject "The researcher" needs "submits", not "submit", in the present tense.
• The sentence speaks of a completed event, so a past form is needed.
  Example: She usually submits her work a day early.

Contrast: the earlier of two past actions takes the past perfect ("had submitted"). The present perfect ("has submitted") links a past action to the present.