The correct answers are: I plan to spend two weeks exploring the Philippines before flying to Japan. After visiting the Netherlands, we'll take a train down to Italy.

We use the definite article "the" with countries that have plural names (like the Philippines, the Netherlands) or include words like "Republic," "Kingdom," or "States" (like the UK). We do not use "the" with singular countries (like Japan or Italy).

We also use "the" with oceans (the Atlantic Ocean), but we do not use it with individual mountains (Mount Everest) or individual lakes (Lake Victoria).