The stock market started November on a strong note as investors reacted to an expansion in US manufacturing last month. The improvement came during what could have been a difficult month for the economy, with a partial government shutdown. The Institute for Supply Management said its manufacturing index rose to 56.4, the highest since April 2011. The positive start to this month’s trading follows a strong October. But some investors are skeptical stocks can keep up this pace. Stocks are also starting to look expensive by some measures. Investors are paying more than $16 for every $1 of earnings in the S&P 500, the most since February 2011.