OG详解-OG3 文法 Q25

Choice A is the best answer. “Currently” logically signals that the archaeologists’ use of drones (a current technology) to photograph the lines is the present-day continuation of the ongoing archaeological research described in the previous sentence. 
Choice B is incorrect because “in comparison” illogically signals that the action described in this sentence offers a comparison to the ongoing archaeological research described in the previous sentence. Instead, the use of drones is the present-day continuation of that research. Choice C is incorrect because “still” illogically signals that the action described in this sentence occurs despite the ongoing archaeological research described in the previous sentence. Instead, the use of drones is the present-day continuation of that research. Choice D is incorrect because “however” illogically signals that the action described in this sentence occurs either despite or in contrast to the ongoing archaeological research described in the previous sentence. Instead, the use of drones is the present-day continuation of that research.