The structure of a molecule is shown below. What is the best estimate for the angle labeled alpha?

Recommended time: $2$ minutes

Slightly less than $109\mathrm{.}5$

$109\mathrm{.}5$

Slightly greater than $109\mathrm{.}5$

Slightly less than $120$

$120$

Slightly greater than $120$

Slightly less than $180$

$180$

Slightly greater than $180$