An indefinite article is used when we are talking generally about something whereas a definite article is used when we are talking about something specific.
The indefinite articles are 'a' and 'an'. An is used before a word starting with a vowel or vowel sound. A is used before a word starting with a consonant or consonant sound.
A definite article is an article that tells the uniqueness of something.
'The' is the only definite article.
The first and last blank shall take 'the' as 'Swiss Alps' represents a specific group/ chain of mountains and 'winter months' represents a specific time. The second blank shall take 'a' as the sentence talks about a particular place. The third and fourth blank won't take any article as 'skiing' is the name of an activity and 'snow' is an uncountable noun.
The correct answer is D) the/a/ no article/ no article/ the.
The Swiss Alps are a good place to go if you like skiing. There is usually plenty of snow during the winter months.