3. The stem-and-leaf plot below shows the average monthly temperatures (${ } ^ { \circ } C$) in Chongqing in 2013:
The median of this data set is\\
A. $19$\\
B. $20$\\
C. $21.5$\\
D. $23$
4. ``$\mathrm { x } > 1$'' is ``$\log _ { \frac { 1 } { 2 } } ( \mathrm { x } + 2 ) < 0$'' a\\
A. necessary and sufficient condition\\
B. sufficient but not necessary condition\\
C. necessary but not sufficient condition\\
D. neither sufficient nor necessary condition\\