O código PHP que imprime a mensagem "abcd

a)

$x = array(?a? => ?b?, ?c? => ?d?); foreach($x as $y){ echo $y; }

b)

$x = array(?a? => ?b?, ?c? => ?d?); foreach($x as $key => $value){ echo $key; }

c)

$x = array(?a? => ?b?, ?c? => ?d?); foreach($x as $key => $value){ echo $value; }

d)

$x = array(?a? => ?b?, ?c? => ?d?); foreach($x as $key => $value){ echo $key.$value; }

e)

$x = array(?a? => ?b?, ?c? => ?d?); foreach($x as $key => $value){ echo $x; }

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