The fish s in the river happyily.“The fish s ”这里填swim还是swimming?

The fish s in the river happyily.“The fish s ”这里填swim还是swimming?
The fish s in the river happyily.
“The fish s ”这里填swim还是swimming?

The fish s in the river happyily.“The fish s ”这里填swim还是swimming?
swim
swimming前要加be动词