为什么输出结果不同？

async function fn1() {
  return 1
}
async function fn2() {
  return Promise.resolve(1)
}

function fn3() {
  return Promise.resolve(1)
}

function fn4() {
  return Promise.resolve(Promise.resolve(1))
}
console.log(fn1()); //Promise {<fulfilled>: 1}
console.log(fn2()); // Promise {<pending>}
console.log(fn3()); // Promise {<fulfilled>: 1}
console.log(fn4()); // Promise {<fulfilled>: 1}