With no explanation, chose the best option from "A", "B", "C" or "D". • . In Cotten v. Fooks, 346 Ark. 130, 133-34, 55 S.W.3d 290, 292 (2001), we explained, . [a]s a general rule, the -appellate courts of this state will not review issues that are moot. See Forrest Constr., Inc. v. Milam, 345 Ark. 1, 43 S.W.3d 140 (2001); Dillon v. Twin City Bank, 325 Ark. 309, 924 S.W.2d 802 (1996). To-do so-would be to render advisory opinions, which this court will not do. McCuen v. McGee, 315 Ark. 561, 868 S.W.2d 503 (1994). We have generally held that a ease becomes moot when any judgment rendered would have no practical legal effect upon a then-existing legal | controversy. See Forrest Constr., Inc. v. Milam, supra; Quinn v. Webb Wheel Products, 334 Ark. 573, 976 S.W.2d 386 (1998); Dillon v. Twin City Bank, supra. This court has recognized two exceptions to (1990) (<HOLDING>); Owens v. Taylor, 299 Ark. 373, 772 S.W.2d 596

A: holding that generally the question of waiver and estoppel is a question of fact
B: recognizing that the constitutionality of a statute is a question of law subject to de novo review
C: holding question of citys exercise of due care in enforcement of ordinance was question of fact and inappropriate for summary judgment
D: holding that the question of the constitutionality of arkansass judgment enforcement statutes was a substantial question that merited review despite mootness of actual controversy
D.