slur|slurred|slurring

他因为太累了，说话开始含糊不清。

He was so tired that he began to ___slur his speech.

他太累了，说话时声音含糊不清。

He was so tired that his speech became ___slurred.

她熬夜工作后，说话开始含糊不清了。

After working all night, she started ___slurring her speech.