Correct answer is Validation modules Is Number operation.
Mule 4 does not use filters anymore. The functionality provided by filters in Mule 3 can be achieved by using the Validation Module.

Choice Router
The Choice router dynamically routes messages through a flow according to a set of DataWeave expressions that evaluate message content. Each expression is associated with a different routing option. The effect is to add conditional processing to a flow, similar to an if/then/else code block in most programming languages.
Only one of the routes in the Choice router executes, meaning that the first expression that evaluates to true triggers that route's execution and the others are not checked. If none of the expressions are true, then the default route executes.
Properties of <when>
PropertyDescription
Expression (expression)
Expression in DataWeave language to evaluate input.
If the expression evaluates to true, this routing option is used:
<when expression="#[vars.language == 'Spanish']" >
Mulesoft Doc Ref : https://docs.mulesoft.com/mule-runtime/4.3/choice-router-concept With respect to above information , Option 1 is the correct syntax as others are incorrect because of below reasons
* Single = is not the correct syntax to validate the condition. It should be ==
* If keyword is not required in when condition.

Correct answer is Merges elements of two lists (arrays) into a single list MuleSoft Doc Reference : https://docs.mulesoft.com/mule-runtime/4.3/dw-core-functions-zip

Correct answer is String is not blank.
------------------------------------------------------------------------------------------------------------------------------------------------- Here's specifically what is happening here:
1) Payload is successfully set to "Start"
2) The Is Blank String validator creates an Error Object because the payload is string "Start". Execution stops
#[error.description] = "String is not blank"
3) Because no error handler is defined, the Mule default error handler handles the error. Remember, at its heart, the Mule Default Error handler is an error handling scope with just an on error propagate
4) "String is not blank" is the error message returned to the requestor in the body of the HTTP requestHTTP Status Code: 500 Reference Diagram:

* Watermark allows the poll scope to poll for new resources instead of getting the same resource over and over again.
* The database table must be ordered so that the "watermark functionality" can move effectively in the ordered list. Watermark stores the current/last picked up "record id."
* If the Mule application is shut down, it will store the last picked up "record id" in the Java Object Store and the data will continue to exist in the file. This watermark functionality is valuable and enables developers to have increased transparency.
* Developers do not need to create code to handle caching; it is all configurable!
* There are two columns and both are unique but user_id can't guaranty sequence whereas date_time will always be in increasing order and table content can easily be ordered on the basis of last processed date_time.
So correct answer is: Set the watermark column to the date_time column