Question

there are the T-shirt对吗

Answer 1

不对的，应该是There is a T-shirt. 或是There are T-shirts. 因为T-shirt是个名词，前面不＋a，后面就要+s。
there is+第三人称单数可数/不可数主语+地点状语（介词短语）；there are+复数主语+地点状语（介词短语）。
1.there is+第三人称单数可数/不可数主语+地点状语（介词短语）

（1）There is a ruler on the desk.书桌上有一把尺。

（2）There is some water in the bottle.瓶子里有一些水。

2.there are+复数主语+地点状语（介词短语）

（1）There are four apples on the tree.树上有四个苹果。
（2）There are many flowers in the park.公园里有许多花。