Three members of a family were killed and three others injured when a truck hit a private car on Dhaka-Khulna Highway at Khankhanapur in Sadar upazila on Sunday.   The deceased were identified as Shuvro Mandal, 33, Lizan Biswas, 6, Shyamol Mandal, 35, of Ballavpur village in Mujibnagar upazila of Meherpur district.   Police said the accident took place around 10:30am when the truck hit the private car carrying six people while heading towards Dhaka, leaving three killed on the spot and three others injured.   The injured were taken to Goalanda Upazila Health Complex.