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

Given two strings s and t, return true if s is a subsequence of t, or false otherwise.
A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not).
 
Please complete the following python code precisely:
```python
class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
```