Which of the following sources is the most reliable, valid source to include in
a historical research paper about the lives of US soldiers fighting in World
War I?
a recent news article about a statue being built on a famous World War I
battlefield
a teacher's lecture on how World War I soldiers routinely dealt with disease and
hunger
O
your great-grandfather's journal, which discusses his time in France as a World
War I soldier
a history textbook that describes troop formations and weaponry employed by
each nation during World War I

the 4th one: your great-grandfather's journal, which discusses his time in France as a World  War I soldier

Explanation:

hope this helps :)

abraham lincoln  (february 12, 1809  – april 15, 1865) was an american statesman, politician, and lawyer who served as the 16th  president of the united states  from 1861 until  his assassination  in april 1865. lincoln led the nation through the  american civil war, its bloodiest war and its greatest moral, constitutional, and political crisis.[2][3]  he preserved the  union,  abolished slavery, strengthened the  federal government, and modernized  the u.s. economy.