Q:Read the following context and choose the correct option to answer the question. Context: On Saturday, President Donald Trump will mark the first anniversary of his inauguration as the 45th president, the day on the steps of the U.S. Capitol he promised to put "America first." Trump's tumultuous first year was unlike that of any other president in recent U.S. history, and 2018 could offer more of the same. The president had his share of victories and setbacks amid a backdrop of Twitter storms and, at times, raging rhetoric. Trump's political base seems pleased with his first year in office, touting his efforts to cut Obama-era regulations, install Justice Neil Gorsuch on the Supreme Court, and roll back Islamic State forces in the Middle East. "We were kind of thinking we were going to relax and put Trump behind us and just watch all the great promises that he gave us, and watch him make America great again," said Michigan Trump supporter Meshawn Maddock. "But what happened immediately is that we felt he was under attack from day one." The president's biggest legislative victory came just last month, a sweeping tax cut bill that had been a Republican priority for years. "We are very proud of it," Trump told reporters in the Oval Office as he signed it. "It is going to be a tremendous thing for the American people. It is going to be fantastic for the economy." In fact, there are plenty of signs of a surging economy, and public opinion polls show growing support for Trump's handling of it and even a bump up in support for the tax bill, which many voters saw initially as too favorable to the wealthy. The tax victory also seems to be helping Trump galvanize the Republican Party behind him, even those who in the past have been cool to his leadership. "This president hasn't even been in office for a year, and look at all the things he has been able to get done, by sheer will in many ways," said Utah Republican Senator Orrin Hatch, who also announced recently he would not run for re-election this year. Question: What is the main cause of President Trump's increase in approval rating? Options: - His tax cut bill - not enough information - His twitter storms - His raging rhetoric
A:
His tax cut bill