不等式$4^x+2^{x+1}-k>0$对$x\in R$恒成立，则k的取值范围是（    ）

Dear Li Fei,
    How are you? I will have a short holiday next week and have decided to visit Shanghai for a second time. I have booked a room in the Peace Hotel. I hear it is on the Bund(外滩) and has a good view of the famous Huangpu River. I will arrive on the night of March 27 and leave early on March 29. I would like to visit some of the most famous places, such as Nanjing Road and Yu Garden in Chenghuangmiao.
    Can you give me some suggestions for my visit to Shanghai? I will have only one day to look around Shanghai. I will be happy if you can make a tour plan for me. Please say hello to Lu Mei. I'm looking forward to your reply.  
Yours,
Sandy

明清时期，民间流传着“湖广熟，天下足”的谚语，这里的“湖广”主要指的是今天的（  ）