It is I who … to blame for the lapses.

Analyze the question: This tests subject-verb agreement in a cleft sentence ("It is I who ..."). The verb after "who" must agree with its antecedent, which is the pronoun "I".

Explain the concept: In the structure "It is I who ...", the relative pronoun "who" refers back to "I". A relative pronoun takes the person and number of its antecedent. Since "I" is first person singular, the verb in the relative clause must be first person singular too.

Solution:

1. The antecedent of "who" is "I" (first person singular).
2. The verb "to be" in the present tense for "I" is am.
3. The sentence becomes: It is I who am to blame for the lapses.

Checking the other options:

• A. was: this is past tense. Nothing in the sentence ("lapses", "to blame") signals past time, and "It is" is present.
• C. is: this agrees with third person singular, not "I".
• D. are: this agrees with plural or "you", not "I".

Correct answer: B (am)

Tip: In "It is I/you/he who ...", look at the pronoun right before "who" and make the verb agree with it:

• It is I who am ...
• It is you who are ...
• It is he who is ...

Whatever comes before "who" decides the verb.