B

Reasoning: Extubation outcome is a categorical (success vs failure) variable being compared between two independent groups (conventional CPAP vs bubble CPAP). The appropriate test for assessing whether the two proportions (90/160 vs 40/160) differ significantly is the Pearson chi-square (or Fisher exact) test for independence of proportions, not paired, t-test, or ANOVA [Fisher et al., 2011, PMID 21536451].