Robert joined as a trainee manager in Lite Apparels, which is the biggest garment factory in California. As soon as he joined, the company$$s union asked him to sign a union security agreement. According to the agreement, he had to pay membership fee of $$500.$ The union$$s demands seem to be a violation of:$$

a$.$ Section $8($b$)(1)($A$).$

b$.$ Section $8($b$)(5).$

c$.$ Section $10($l$).$

d$.$ Section $8($b$)(6).$