With no explanation, chose the best option from "A", "B", "C" or "D". Co., 305 F.3d 1210, 1221 (10th Cir. 2002) (internal quotation marks omitted). We have held that a plaintiff cannot prove a causal connection when the decision maker took the challenged employment action without knowledge that the plaintiff was taking FMLA leave. Sabourin v. Univ. of Utah, 676 F.3d 950, 958-59 (10th Cir. 2012); see also Didier v. Abbott Labs., 614 Fed.Appx. 366, 378 (10th Cir. 2015) (upholding summary judgment dismissal of FMLA retaliation claim because the plaintiff did not present evidence that the persons responsible for terminating her knew she was taking FMLA leave). If knowledge is lacking, then the protected activity cannot be said to have caused the adverse employment action. Jones v. United Parcel Serv., Inc., 502 F.3d 1176, 1195 (10th Cir. 2007) (<HOLDING>). Ms. Utter argues an employer can be hable for

A: holding that whether an employee decides to assist the charging party or refuses to assist the  employer the employer may not retaliate against the employee because this decision of the employee constitutes participation in an investigation or proceeding under title vii
B: holding in an americans with disability act retaliation action that ujnless an employer knows that an employee is engaging in protected activity it cannot retaliate against that employee because of the protected conduct
C: holding that communications with the fbi were protected under the first amendment because prior to 1986 the law was clear that an employer may not retaliate against an employee for expressing his views about matters of public concern
D: holding that for purposes of a title vii retaliation claim an action is cognizable as an adverse employment action if it is reasonably likely to deter employees from engaging in protected activity
B.