The correct answer is (a) 90 days.
The President of the Philippines is elected to a six-year term. If the President dies, resigns, or is removed from office, the Vice President becomes President. If the Vice President is also unable to serve, the President of the Senate becomes President. If the President of the Senate is also unable to serve, the Speaker of the House of Representatives becomes President.
The vacancy of the Office of the President must be filled up within 90 days. If the vacancy occurs during the last two years of the President’s term, the Vice President or the next in line to the presidency will serve for the remaining two years. If the vacancy occurs during the first four years of the President’s term, a special election will be held to fill the vacancy.
Option (b), six months, is incorrect. The vacancy of the Office of the President must be filled up within 90 days, not six months.
Option (c), nine months, is incorrect. The vacancy of the Office of the President must be filled up within 90 days, not nine months.
Option (d), one year, is incorrect. The vacancy of the Office of the President must be filled up within 90 days, not one year.