Answer: Choice B
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Step-by-step explanation:
Choice A can be ruled out because the three angles shown add up to 360 degrees (which is a full circle rotation). The three angles of any triangle always add to 180.
Choice C can be ruled out because angles 'a' and 'b' are supplementary, as they same side interior angles. Because a+b = 180, there isn't any way to have c be a positive number and have a+b+c = 180 to be true. In other words, angles a,b,c add up to something over 180 degrees.
Choice D is a similar story to choice C. The three angles a,b,c add up to something over 180 degrees, but less than 360.
Choice B is the only thing left. We can see that the three angles form a straight angle, so a+b+c = 180 is true and all three variables are positive numbers. If b = c were true, then the triangle is isosceles. This is because the base angles are always congruent for any isosceles triangle.
That's why choice B is the answer.