What do you need help on exactly?
Given:
A company wants to select 1 project from a set of 4 possible projects.
Consider the options are:
a.
b.
c.
d. 
To find:
The constraints that ensures only 1 will be selected.
Solution:
It is given that the company wants to select 1 project from a set of 4 possible projects. It means the sum of selected projects must be equal to 1.

Therefore, the correct option is (a).
A triangle with sides measuring 300, 400 and 700 because 300+400+700=1400 which is higher than the first triangle 300+400+500=1200