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How to use the verb ARIMASU (Lesson 7)
ARIMASU (There is, There are) belongs to what we call "stative verbs," the verbs that describe the states in which people or things are. ARIMASU takes GA as the particle that indicates the subject.Essentially, we use GA, when we introduce a person or a thing into our conversation for the first time.
That's why, when Anna entered the cake shop, she said KÊKI GA IPPAI ARIMASU NE (There are lots of cakes). Here, "cakes" are the subject, and she mentioned them for the first time here.

Here is another example. Suppose you go to a shop to buy shirts, but can’t find L-sized shirts. So, you ask a clerk ERU SAIZU WA ARIMASU KA (Are there any L-sized shirts?).