error CS1525: Unexpected symbol `??'

Hey guys! iam trying to create a building placement script but i have a weird error: Assets/Script/BuildingPlacement.cs(30,66): error CS1525: Unexpected symbol ??', expecting identifier'

here is the code: maybe you can have a look over it and help me out?

 using UnityEngine;
 using System.Collections;
 
 public class BuildingPlacement : MonoBehaviour {
 
     public float scrollSensitivity;
         
     private PlaceableBuilding placeableBuilding;
     private Transform  currentBuilding;
     private bool hasPlaced;
     
     public LayerMask buildingsMask;
     
     private PlaceableBuilding placeableBuildingOld;
     
     public float speed = 30; 
     
     
     // Update is called once per frame
     void Update () {
     
         //Vector3 m = Input.mousePosition;
         //m = new Vector3(m.x,m.y,transform.position.y);
         //Vector3 p = camera.ScreenToWorldPoint(m);
         
         if (currentBuilding != null && !hasPlaced){
             //rotate object
             //var speed = 30;
             RaycastHit hit = new RaycastHit();
             Ray ray = camera.ScreenPointToRay(Input.­mousePosition);
             Physics.Raycast(ray,out hit, Mathf.Infinity, groundMask);
             
             if (Input.GetKey(KeyCode.A))
             currentBuilding.transform.Rotate(Vector3.down * speed * Time.deltaTime);
             
             //currentBuilding.position = new Vector3(p.x,0,p.z);
             currentBuilding.position = hit.point;
             
             if (Input.GetMouseButtonDown(0)) {
                 if (IsLegalPosition()) {
                     hasPlaced = true;
                 }
             }
         }
         else {
             if (Input.GetMouseButtonDown(0)) {
                 RaycastHit hit = new RaycastHit();
                 Ray ray = new Ray(new Vector3(p.x,8,p.z), Vector3.down);
                 if (Physics.Raycast(ray, out hit,Mathf.Infinity,buildingsMask)) {
                     if (placeableBuildingOld != null) {
                         placeableBuildingOld.SetSelected(false);
                     }
                     hit.collider.gameObject.GetComponent<PlaceableBuilding>().SetSelected(true);
                     placeableBuildingOld = hit.collider.gameObject.GetComponent<PlaceableBuilding>();
                 }
                 else {
                     if (placeableBuildingOld !=null) {
                         placeableBuildingOld.SetSelected(false);
                     }
                 }
             }
         }
     }
 
     bool IsLegalPosition() {
         if (placeableBuilding.colliders.Count > 0) {
             return false;
         }
         return true;
     }
     
     public void SetItem(GameObject b) {
         hasPlaced = false;
         currentBuilding = ((GameObject)Instantiate(b)).transform;
         placeableBuilding = currentBuilding.GetComponent<PlaceableBuilding>();
     }
 }

thanks for any hint :)