When did Rick Gates plead guilty to lying to prosecutors and commenced cooperation with the investigation?

Choices:
A. not enough information
B. after Paul Manafort pleaded not guilty to charges brought by Robert Mueller.
C. at the beginning of the investigation launch
D. after 13 Russians were indicted in connection with election meddling
after 13 Russians were indicted in connection with election meddling
In recent weeks, the investigation into possible collusion between President Donald Trump’s presidential campaign and Russia has intensified, raising the prospect that the probe could become an issue in advance of the November midterm congressional elections.
Former Trump campaign manager Paul Manafort made another appearance in federal court in Washington Wednesday, where he pleaded not guilty to the latest round of charges brought by special counsel Robert Mueller.

Last week, Rick Gates, Manafort’s former deputy, pleaded guilty to lying to prosecutors and is now cooperating with the investigation.
In mid-February, 13 Russians were indicted in connection with election meddling, which deputy attorney general Rod Rosenstein described as an effort to “promote discord in the United States and undermine public confidence in democracy. We must not allow them to succeed.”
Congressional inquiries also continue. Hope Hicks, the White House communications director and a longtime Trump aide, was the latest figure to testify before a congressional committee on the Russia probe.
Hicks declined to answer some questions before a closed session of the House Intelligence Committee, frustrating several Democrats.
“This is not executive privilege. This is executive stonewalling,” said ranking committee Democrat Rep. Adam Schiff.

But there was more pushback from the White House this week. President Trump fired off a series of tweets dismissing the probe as a “WITCH HUNT.”
“They have had this phony cloud over this administration, over our government,” Trump told reporters at the White House last month. “And it has hurt our government, it does hurt our government. It is a Democrat hoax.”
Democrats reject that view, including Sen. Mark Warner, the top Democrat on the Senate Intelligence Committee.
“I continue to believe that this is the most important thing that I will work on in my whole public career, and getting the whole truth out is extraordinarily important,” he said.

Warner’s committee is also investigating possible collusion between the Trump campaign and Russia, an issue that has cast a cloud over the White House since Trump took office.