WPP Chief Executive Martin Sorrell has said second quarter trading could surpass its robust set of results in the previous three months."I think we are stronger than the first quarter," he said in an interview with Reuters at the Cannes Lions advertising festival. "April was strong, May was not as strong as April but satisfactory, and at the revenue level very strong. The second quarter if anything will be the same or better than the first quarter."His remarks come after the world's largest advertising group reported a better-than-expected 7% increase if first quarter revenue, driven by new client wins.RD