there be句型的句子成分怎么分析？

There be陈述句句型，常表示某处（某地）存在有某人或某物。 一、结构句型：there be（are/is/ was /were）+主语+介词短语...... (1) there is+单数可数名词/ 不可数名词+地点短语...... There is a ruler on the desk.书桌上有一把尺。 (2) there are+复数名词+地点短语...... There are four apples on the tree.（长在树