Airline: Newly developed collision-avoidance systems, although not ful

Airline: Newly developed collision-avoidance systems, although not fully tested to discover potential malfunctions, must be installed immediately in passenger planes. Their mechanical warnings enable pilots to avoid crashes.

Pilots: Pilots will not fly in planes with collision-avoidance systems that are not fully tested. Malfunctioning systems could mislead pilots, causing crashes.

The pilots objection is most strengthened if which of the following is true?

(A) It is always possible for mechanical devices to malfunction.
This option is talking about all the mechanical devices in general. But our argument is concerned specifically with the Newly developed collision-avoidance systems. Just on the basis of these collision-avoidance system not being fully tested, we cannot make such a broad conclusion/statement about all the mechanical devices.
Also, this option is talking about the possibility, which may or may not be true. But option C converts the possibility to a definite assurance. So, C is the best choice.
One more important point to note here is MECHANICAL DEVICES, again this option is very broad. Because it has not differentiated the fully tested AND not fully tested devices. The argument is concerned with the 'NOT FULLY TESTED NEWLY DEVELOPED COLLISION AVOIDANCE SYSTEMS'.

(B) Jet engines, although not fully tested when first put into use, have achieved exemplary performance and safety records.
The argument is concerned with newly developed collision-avoidance systems and this option statement is talking about Jet Engines. We are not at all concerned with the exemplary performance and safety records of the Jet engines. So, No Impact.

(C) Although collision-avoidance systems will enable pilots to avoid some crashes, the likely malfunctions of the not-fully-tested systems will cause even more crashes.
Correct, goes in line with the pilots objection.
Choice C states that what the pilots think could happen is likely to happen. Thus, C is the best choice.
Pilots: Malfunctioning systems could mislead pilots, causing crashes.
Option C: The likely malfunctions of the not-fully-tested systems will cause even more crashes.
This option C is giving complete assurance that collisions/crashes will happen for sure because of these malfunctioning systems which are not fully tested.

(D) Many airline collisions are caused in part by the exhaustion of overworked pilots.
It is suggesting a different cause instead of supporting the pilots objection. It weakens. Exhaustion of overworked pilots is a different cause altogether. So, incorrect.
Malfunctioning systems causing crashes/collisions is the main concern of the pilots objection.

(E) Collision-avoidance systems, at this stage of development, appear to have worked better in passenger planes than in cargo planes during experimental flights made over a six-month period.
so what? At this stage of development, collision-avoidance systems are still not fully tested. So, Malfunctioning systems could mislead pilots, and can still cause crashes/collisions. So, incorrect.
Also, this option only suggests that systems have worked better in passenger planes than cargo planes, but still no assurance for the proof that these systems will not malfunction.
Comparison with cargo planes, is also irrelevant.