A group of manufacturers of LCD screens for computers and cell phones met together monthly in private conference rooms in hotels to discuss their markets and kept notes with phrases such as "Must act together with the Korean makers in order to reap success," and "Extremely confidential.Must not distribute."The result was that the LCD screen producers were able to command high prices for their products, prices that were non-negotiable.Which of the following statements is correct about their conduct?

a.The manufacturers had engaged in aper seviolation of antitrust laws.

b.The manufacturers violated the Sherman Act.

c.The manufacturers violated the Clayton Act.

d.both a and be.all of the above