Who were the first 20 presidents in alphabetical order?

First 20 presidents in alphabetical order:

Adams, John (1797-1801)  

Adams, John Quincy (1825-1829)  

Arthur, Chester Alan (1881-1885)  

Buchanan, James (1857-1861)

Bush, George (1989-1993 )  

Bush George W. (2001-2009)  

Carter, Jimmy (1977-1981)  

Cleveland, Grover (1885-1889, 1893-1897)  

Clinton, Bill (1993-2001)  

Coolidge, Calvin (1923-1929)  

Eisenhower, Dwight D. (1953-1961)  

Fillmore, Millard (1850-1853)  

Ford, Gerald R. (1974-1977)  

Garfield, James A. (1881)  

Grant, Ulysses S. (1869-1877)  

Harding, Warren G. (1921-1923)  

Harrison, Benjamin (1889-1893)  

Harrison, William Henry (1841)  

Hayes, Rutherford Birchard (1877-1881)  

Hoover, Herbert (1929-1933)  

Jackson, Andrew (1829-1837)  

Jefferson, Thomas (1801-1809)  

Johnson, Andrew (1865-1869)  

Johnson, Lyndon B. (1963-1969)  

Kennedy, John F. (1961-1963)  

Lincoln, Abraham (1861-1865)  

Madison, James (1809-1817)  

McKinley, William (1897-1901)  

Monroe, James (1817-1825)  

Nixon, Richard M. (1969-1974)  

Obama, Barack (2009-2017)  

Pierce, Franklin (1853-1857)  

Polk, James K. (1845-1849)  

Reagan, Ronald (1981-1989)  

Roosevelt, Franklin D. (1933-1945)  

Roosevelt, Theodore (1901-1909)  

Taft, William H. (1909-1913)  

Taylor, Zachary (1849-1850)  

Truman, Harry S. (1945-1953)  

Trump, Donald J. (2017- )  

Tyler, John (1841-1845)  

Van Buren, Martin (1837-1841)  

Washington, George (1789-1797)  

Wilson, Woodrow (1913-1921)  

c, they united with once

the correct answer is d