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The question has a set of four statements. Each statement has three segments. Choose the alternative where the third segment in the statement can be logically deduced using both the preceding two, but not just from one of them.

1. Dinosaurs are prehistoric creatures. Water-buffaloes are not dinosaurs. Water-buffaloes are not prehistoric creatures.
2. All politicians are frank. No frank people are crocodiles. No crocodiles are politicians.
3. No diamond is quartz. No opal is quartz. Diamonds are opals.
4. All monkeys like bananas. Some GI Joes like bananas. Some GI Joes are monkeys.
1. C only
2. B only
3. A and D
4. B and C

from deduction rules http://aptitude.gateoverflow.in/2346/cat1999-125#a2370

$\text{Option (A)}:$

1. Dinosaurs are prehistoric creatures , dinosaurs distributed term , prehisoric creatures non distributed $(2.1)$
2. Water-buffaloes are not dinosaurs.here  water buffaloes non distributed , dinosaurs distributed $(2.4)$

Given conclusion : Water-buffaloes are not prehistoric creatures. $\textbf{which is not correct,}$ here prehistoric creature should be non distributed bcoz in premise it is non distributed but in conclustion from $2.4$ prehistoric creature is distributed so $\text{it violate 7th rule}$

$\text{Option (B)}:$

1. All politicians are frank.
2. No frank people are crocodiles.

Given conclusion : "No crocodiles are politicians"  $\textbf{this is correct,}$ following all rules$\dots$

$\text{Option (C)}:$

1. No diamond is quartz.
2. No opal is quartz.

Given conclusion : Diamonds are opals.  here no conclusion exist beoz of $\text{rule (5)}$ if both premises are negative then no conclusion. so, $\textbf{it is not correct.}$

$\text{Option (D)}:$

1. All monkeys like bananas , monkey distributed , bananas not distributed $(2.1)$
2. Some GI Joes like bananas GI ,bananas both are not distributed $(2.2)$

Given conclusion : Some GI Joes are monkeys  , there is no conclusion , here middle term bananas which must be distributed once , but in both premise bananas is not distributrd term so $\text{it violate rule 2}.$ so, $\textbf{it is not correct.}$

hence only $\text{B}$ is correct Answer.

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