Please solve the programming task below using a self-contained code snippet in a markdown code block.

A pangram is a sentence where every letter of the English alphabet appears at least once.
Given a string sentence containing only lowercase English letters, return true if sentence is a pangram, or false otherwise.
 
Please complete the following python code precisely:
```python
class Solution:
    def checkIfPangram(self, sentence: str) -> bool:
```