Table:
0
A
B
C
D
E
1
Game
Date
Opponent
Score
Record
2
24
12/1/1973
Seattle SuperSonics
120 - 110
13 - 11
3
25
12/5/1973
at Kansas City Kings
105 - 117
13 - 12
4
26
12/7/1973
at Boston Celtics
112 - 116
13 - 13
5
27
12/8/1973
at New York Knicks
100 - 117
13 - 14
6
28
12/11/1973
Buffalo Braves
127 - 132
13 - 15
7
29
12/15/1973
at Milwaukee Bucks
82 - 116
13 - 16
8
30
12/18/1973
at Capital Bullets
98 - 91
14 - 16
9
31
12/19/1973
New York Knicks
107 - 105
15 - 16
10
32
12/21/1973
at Houston Rockets
124 - 110
16 - 16
11
33
12/22/1973
Cleveland Cavaliers
98 - 108
16 - 17
12
34
12/26/1973
Philadelphia 76ers
145 - 118
17 - 17
13
35
12/28/1973
at Chicago Bulls
94 - 118
17 - 18
14
36
12/29/1973
Houston Rockets
114 - 110
18 - 18
15
37
12/30/1973
at Cleveland Cavaliers
99 - 94
19 - 18

Questions and formulas:
Question: Who did the Hawks play on 12/21/1973?
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,B1="12/21/1973"),3))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E15,B2:B15="12/21/1973"),3))
Level: medium