小题1:There is a dog behind the door.

小题2:Don’t spit on the floor.

小题3:He would rather go swimming than watch TV at home.

小题4:We plant trees in spring.

小题5:He was really tired when he finished his homework at twelve o’clock.

题目分析：

小题1:根据图片及所给词可知，门后有一只狗。应用there be结构，故应写为：There is a dog behind the door.

小题2:根据图片及所给词可知，这是一张警示牌，表示禁止随地吐痰。应用祈使句。故应写为：Don’t spit on the floor.。

小题3:根据图片及所给词可知，他宁愿去游泳也不愿在家看电视。Would rather do sth than do sth：表示宁可做某事也不愿做某事。故应写为：He would rather go swimming than watch TV at home.

小题4:根据图片及所给词可知，我们在春季植树。故应写为：We plant trees in spring.

小题5:根据图片及所给词可知，当他12点钟完成作业后真的感到累了。结合语境，应用一般过去时，故应写为：He was really tired when he finished his homework at twelve o’clock