How did Benjamin Graham view stock investment a. He believed that both trading stocks and investing stocks are risky. b. He regarded investing stocks equally risky as trading stocks. c. He insisted that trading stocks were less valuable than investing stocks. d. He compared hot stocks to fashionable dogs.

李白的《古意》中写道：“君为女萝草，妾作菟丝花。”请问古人常用“萝草”和“菟丝花”比喻什么？