Learning JSON-LD - some questions

I have the following JSON-LD document:

[
    {
        "@context": {
            "tt": "http://my-company-name/Tasking#",
            "task": "http://my-company-name/data/TaskingOntology#",
            "rdfs": "http://www.w3.org/2000/01/rdf-schema#"
        },
        "@id": "tt:Task_3",
        "@type": "task:Task",
        "task:itemToTeardown": {
                "@id": "tt:TaskSubject"
        },
        "task:taskDescription": {
                "@value": "The description of the task"
        },
        "rdfs:label": {
                "@value": "Task 3"
        }
    },
    {
        "@context": {
            "tt": "http://my-company-name/Tasking#",
            "task": "http://my-company-name/data/TaskingOntology#",
            "rdfs": "http://www.w3.org/2000/01/rdf-schema#"
        },
        "@id": "tt:taskparta_TaskSubject",
        "task:isComponentOf": {
                "@id": "task:TaskSubject"
        },
        "rdfs:label": {
                "@value": "Label A"
        }
    },
    {
        "@context": {
            "tt": "http://my-company-name/Tasking#",
            "task": "http://my-company-name/data/TaskingOntology#",
            "rdfs": "http://www.w3.org/2000/01/rdf-schema#"
        },
        "@id": "tt:taskpartb_TaskSubject",
        "task:isComponentOf": {
                "@id": "task:TaskSubject"
        },
        "rdfs:label": {
                "@value": "Label B"
        }
    }
]


using https://github.com/RDFLib/rdflib-jsonld, it will produce the
following RDF:

@prefix ns1: <http://my-company-name/data/TaskingOntology#> .

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .

@prefix xml: <http://www.w3.org/XML/1998/namespace> .

@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .


<http://my-company-name/Tasking#Task_3> a ns1:Task ;

    rdfs:label "Task 3" ;

    ns1:itemToTeardown <http://my-company-name/Tasking#TaskSubject> ;

    ns1:taskDescription "The description of the task" .


<http://my-company-name/Tasking#taskparta_TaskSubject> rdfs:label "Label A" ;

    ns1:isComponentOf ns1:TaskSubject .


<http://my-company-name/Tasking#taskpartb_TaskSubject> rdfs:label "Label B" ;

    ns1:isComponentOf ns1:TaskSubject .


I have the following questions:

(1) I need to duplicate the @context across several entries. Is there some
way to avoid that? I note that in the RDF, the common prefixes can be
shared.

(2) Does the JSON-LD stuff look "right"? Does anything smell? It is hard
for me to judge having only starting looking at such things.

(3) In the RDF, I see <http://my-company-name/Tasking#Task_3> *a* ns1:Task
; ... what is the 'a'? Where did it come from?

Thank you.