Problem to build a SQL query with the queryBuilder

A.php

<?php

class A
{

    /**
     * @var ArrayCollection
     *
     * @ORM\OneToMany(targetEntity="B", mappedBy="")
     * @Assert\Valid(traverse=true)
     */
    private $Bs;
    ...
}

ARepository.php

<?php
...

$queryBuilder = $this->createQueryBuilder('A')
                     ->leftJoin('A.B', 'B')
                     ->andWhere('B.v = plop')
                     ->addSelect('B') //If i remove this line, i have a error show below
                     ->leftJoin('B.C', 'C')
                     ->andWhere('C.v = plop')
                     ->addSelect('C');

/* 
If i remove "->addSelect('B')" i get this error:
The parent object of entity result with alias 'C' was not found. The parent alias is 'B'. 


*/

B.php

<?php

class B
{
    /**
     * @var A
     *
     * @ORM\ManyToOne(targetEntity="A", inversedBy="Bs")
     */
    private $ownerA;

    /**
     * @var C
     *
     * @ORM\OneToMany(targetEntity="C")
     */
    private $Bs;

    /**
     * @var string
     *
     * @ORM\Column(name="v", type="string", length=255)
     */
    private $v;

    ...
}

C.php

class C
{
    /**
     * @var string
     *
     * @ORM\Column(name="v", type="string", length=255)
     */
    private $v;

    ...
}