**Explanation:**

The absorption at 1380 cm-1 indicates the presence of a C-H bond in the compound. Let's analyze each option to determine which compound has a C-H bond that shows absorption at 1380 cm-1.

**a) 2-Methyl-1-butene:**
2-Methyl-1-butene has the molecular formula C5H10. This compound contains two types of C-H bonds, one in the methyl group and another in the methylene group. However, the absorption at 1380 cm-1 is not expected for either of these C-H bonds. Therefore, option a) is not the correct answer.

**b) Cyclopentane:**
Cyclopentane has the molecular formula C5H10. In this compound, all the carbon atoms are sp3 hybridized and have C-H bonds. The absorption at 1380 cm-1 can be attributed to the C-H bonds in cyclopentane. The absorption at this wavenumber is characteristic of the C-H bending vibration in a cycloalkane. Therefore, option b) is the correct answer.

**c) Pentyne:**
Pentyne has the molecular formula C5H10. This compound contains a triple bond between two carbon atoms, and the remaining carbon atoms are sp3 hybridized. The absorption at 1380 cm-1 is not expected for either the triple bond or the sp3 C-H bonds. Therefore, option c) is not the correct answer.

**d) Methylcyclobutane:**
Methylcyclobutane has the molecular formula C5H10. In this compound, there are both cycloalkane and alkane moieties. The absorption at 1380 cm-1 can be attributed to the C-H bonds in the cycloalkane ring, similar to cyclopentane. Therefore, option d) is not the correct answer.

Based on the analysis, the correct answer is **b) Cyclopentane**, as it is the only compound that has C-H bonds showing an absorption at 1380 cm-1.