请用视频方式讲述这道题的解题过程---**Extracted Content:**
**Question Number:** 15
**Question Stem:**
在3×3方格表的9个单元格中放置△或○，下图是一种有三个△在一条线上的放置方法。问：有三个△在一条线上，并且有三个○在一条线上的放置方法有多少种？
*Translation:* Place △ or ○ in the 9 cells of a 3×3 grid. The figure below shows a placement method where three △ are in a line. Question: How many placement methods are there where there are three △ in a line AND three ○ in a line?
**Options:**
(A) 39
(B) 42
(C) 78
(D) 84
(E) 96
**Chart/Diagram Description:**
* **Type:** Grid / Table
* **Main Elements:**
* A 3x3 square grid is displayed, containing 9 cells.
* Each cell contains either a triangle (△) or a circle (○).
* The arrangement of symbols in the grid is as follows:
* Row 1: Triangle (△), Circle (○), Triangle (△)
* Row 2: Triangle (△), Circle (○), Triangle (△)
* Row 3: Triangle (△), Triangle (△), Circle (○)
* An observation of the image reveals that the first column contains three triangles in a line (△, △, △).