Part l: Each for $4$ points.

Note: Circle one answer, ONLY. If you circle $2$ or more, you won't receive any points.

Consider the following Bode plot of a system. What are the approximate values of crossover frequency, ${}_c,$ gain margin, GM$,$ and phase margin, PM$,$ of the system?

a$){}_c=1\mathrm{.}2ra\frac{d}{s},PM<mn>0</mn><mtext></mtext><mi>(</mi>$system is unstable$)$

b$){}_c=1\mathrm{.}2ra\frac{d}{s},GM$~~$15dB,PM$~~$112$

c$){}_c=1\mathrm{.}8ra\frac{d}{s},GM<mn>0</mn><mtext></mtext><mi>(</mi>$system is unstable$)$

d$){}_c=3\mathrm{.}5ra\frac{d}{s},GM$~~$15dB,PM$~~$112$

e$){}_c=3\mathrm{.}5ra\frac{d}{s},GM$~~$7\mathrm{.}4dB,PM$~~$30$

f$){}_c=5\mathrm{.}5ra\frac{d}{s},GM$~~$7\mathrm{.}4dB,PM$~~$30$