Question

markers of scientific inquiry remain: in astronomy, there is ptolemy’s almagest; in medicine, hippocratic case notes; and in optics, ibn al - haytham’s treatises. perhaps the most enduring feature shared by these works ___ their systematic reliance on observation and reasoned explanation, establishing methods of inquiry.
which choice completes the text so that it conforms to the conventions of standard english?
a is
b are
c was
d were

Explanation:

To solve this, we analyze the subject-verb agreement. The subject here is "the most enduring feature", which is singular. Also, the context (mention of "remain" and present - day references like Ptolemy’s, Hippocratic, Ibn al - Haytham’s works) indicates present tense. So we need a singular present - tense verb. Option A "is" is singular and present - tense, while B is plural, C and D are past - tense.

Answer:

A. is