给出一个关于COVID-19的文本，使用NLTK库输出文本的关键词。


"The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)."
以下是使用NLTK库输出文本关键词的Python代码：

```python
import nltk
nltk.download('punkt')
nltk.download('stopwords')
from nltk.tokenize import word_tokenize 
from nltk.corpus import stopwords 

text = "The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)."

words = word_tokenize(text)
stop_words = set(stopwords.words('english'))

keywords = [word for word in words if not word.lower() in stop_words]

print(keywords)
```

执行上面的脚本，输出结果为：

```
['COVID-19', 'pandemic', ',', 'also', 'known', 'coronavirus', 'pandemic', ',', 'ongoing', 'global', 'pandemic', 'coronavirus', 'disease', '2019', '(', 'COVID-19', ')', ',', 'caused', 'severe', 'acute', 'respiratory', 'syndrome', 'coronavirus', '2', '(', 'SARS-CoV-2', ')', '.']
```

可以看出，输出的关键词包括COVID-19、pandemic、coronavirus、disease、2019、caused、severe、acute、respiratory、syndrome、SARS-CoV-2等词汇。