So how to judge whether the subject is "Shansan"? Let's distinguish between singular and plural first. If it is singular, such as Lucy, ask yourself a few questions: 1. Is this (Lucy here) me? Answer: No.2. Is this (Lucy is here) "you"? Answer: No, at this time we can know that Lucy is "Shanshan". When Lucy is the subject, the predicate verb will be in the form of "Shansan". Lucy is very popular with us.
There is also an uncountable noun as the subject, which can also be regarded as "single three"
Water is good for all of us.
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Of course, there are other places to pay attention to, but with the deepening of your study, you will gradually get in touch with and master it. I suggest you read a simple grammar book, which is very helpful for your improvement.