plot应用

> x1 <- c(35, 40, 40, 42, 37, 45, 43, 37, 44, 42, 41, 39)

> x2 <- c(60, 74, 64, 71, 72, 68, 78, 66, 70, 65, 73, 75)

> plot(x1, x2)

> plot(x1, x2, main=“胸围与体重”, xlab="胸围", ylab="体重", clo="blue", pch=17)

Error: unexpected input in "plot(x1, x2, main=?

为什么不行呢？