function fn_1() {
	var img_1 = document.getElementById("pic_img_1");
	var img_2 = document.getElementById("pic_img_2");
	var div_1 = document.getElementById("know_cont_1");
	var div_2 = document.getElementById("know_cont_2");
	img_1.src = "images/icons/title_know_1.jpg";
	img_2.src = "images/icons/title_know_3.jpg";
	div_1.style.display = "block";
	div_2.style.display = "none";
	}
function fn_2() {
	var img_1 = document.getElementById("pic_img_1");
	var img_2 = document.getElementById("pic_img_2");
	var div_1 = document.getElementById("know_cont_1");
	var div_2 = document.getElementById("know_cont_2");
	img_1.src = "images/icons/title_know_2.jpg";
	img_2.src = "images/icons/title_know_4.jpg";
	div_1.style.display = "none";
	div_2.style.display = "block";
	}