2. Heidi is $2.1 \mathrm{~m}$ tall, while Lola is only $1.4 \mathrm{~m}$ tall. What is their average height?

A $1.525 \mathrm{~m}$
B $\quad 1.6 \mathrm{~m}$
C $\quad 1.7 \mathrm{~m}$
D $1.725 \mathrm{~m}$
E $1.75 \mathrm{~m}$